two version of R2R are hereHEADmaster

1 files changed, 761 insertions, 0 deletions

diff --git a/.venv/lib/python3.12/site-packages/email_validator/syntax.py b/.venv/lib/python3.12/site-packages/email_validator/syntax.py
new file mode 100644
index 00000000..c6554518
--- /dev/null
+++ b/.venv/lib/python3.12/site-packages/email_validator/syntax.py
@@ -0,0 +1,761 @@
+from .exceptions_types import EmailSyntaxError, ValidatedEmail
+from .rfc_constants import EMAIL_MAX_LENGTH, LOCAL_PART_MAX_LENGTH, DOMAIN_MAX_LENGTH, \
+    DOT_ATOM_TEXT, DOT_ATOM_TEXT_INTL, ATEXT_RE, ATEXT_INTL_DOT_RE, ATEXT_HOSTNAME_INTL, QTEXT_INTL, \
+    DNS_LABEL_LENGTH_LIMIT, DOT_ATOM_TEXT_HOSTNAME, DOMAIN_NAME_REGEX, DOMAIN_LITERAL_CHARS
+
+import re
+import unicodedata
+import idna  # implements IDNA 2008; Python's codec is only IDNA 2003
+import ipaddress
+from typing import Optional, Tuple, TypedDict, Union
+
+
+def split_email(email: str) -> Tuple[Optional[str], str, str, bool]:
+    # Return the display name, unescaped local part, and domain part
+    # of the address, and whether the local part was quoted. If no
+    # display name was present and angle brackets do not surround
+    # the address, display name will be None; otherwise, it will be
+    # set to the display name or the empty string if there were
+    # angle brackets but no display name.
+
+    # Typical email addresses have a single @-sign and no quote
+    # characters, but the awkward "quoted string" local part form
+    # (RFC 5321 4.1.2) allows @-signs and escaped quotes to appear
+    # in the local part if the local part is quoted.
+
+    # A `display name <addr>` format is also present in MIME messages
+    # (RFC 5322 3.4) and this format is also often recognized in
+    # mail UIs. It's not allowed in SMTP commands or in typical web
+    # login forms, but parsing it has been requested, so it's done
+    # here as a convenience. It's implemented in the spirit but not
+    # the letter of RFC 5322 3.4 because MIME messages allow newlines
+    # and comments as a part of the CFWS rule, but this is typically
+    # not allowed in mail UIs (although comment syntax was requested
+    # once too).
+    #
+    # Display names are either basic characters (the same basic characters
+    # permitted in email addresses, but periods are not allowed and spaces
+    # are allowed; see RFC 5322 Appendix A.1.2), or or a quoted string with
+    # the same rules as a quoted local part. (Multiple quoted strings might
+    # be allowed? Unclear.) Optional space (RFC 5322 3.4 CFWS) and then the
+    # email address follows in angle brackets.
+    #
+    # An initial quote is ambiguous between starting a display name or
+    # a quoted local part --- fun.
+    #
+    # We assume the input string is already stripped of leading and
+    # trailing CFWS.
+
+    def split_string_at_unquoted_special(text: str, specials: Tuple[str, ...]) -> Tuple[str, str]:
+        # Split the string at the first character in specials (an @-sign
+        # or left angle bracket) that does not occur within quotes and
+        # is not followed by a Unicode combining character.
+        # If no special character is found, raise an error.
+        inside_quote = False
+        escaped = False
+        left_part = ""
+        for i, c in enumerate(text):
+            # < plus U+0338 (Combining Long Solidus Overlay) normalizes to
+            # ≮ U+226E (Not Less-Than), and  it would be confusing to treat
+            # the < as the start of "<email>" syntax in that case. Liekwise,
+            # if anything combines with an @ or ", we should probably not
+            # treat it as a special character.
+            if unicodedata.normalize("NFC", text[i:])[0] != c:
+                left_part += c
+
+            elif inside_quote:
+                left_part += c
+                if c == '\\' and not escaped:
+                    escaped = True
+                elif c == '"' and not escaped:
+                    # The only way to exit the quote is an unescaped quote.
+                    inside_quote = False
+                    escaped = False
+                else:
+                    escaped = False
+            elif c == '"':
+                left_part += c
+                inside_quote = True
+            elif c in specials:
+                # When unquoted, stop before a special character.
+                break
+            else:
+                left_part += c
+
+        if len(left_part) == len(text):
+            raise EmailSyntaxError("An email address must have an @-sign.")
+
+        # The right part is whatever is left.
+        right_part = text[len(left_part):]
+
+        return left_part, right_part
+
+    def unquote_quoted_string(text: str) -> Tuple[str, bool]:
+        # Remove surrounding quotes and unescape escaped backslashes
+        # and quotes. Escapes are parsed liberally. I think only
+        # backslashes and quotes can be escaped but we'll allow anything
+        # to be.
+        quoted = False
+        escaped = False
+        value = ""
+        for i, c in enumerate(text):
+            if quoted:
+                if escaped:
+                    value += c
+                    escaped = False
+                elif c == '\\':
+                    escaped = True
+                elif c == '"':
+                    if i != len(text) - 1:
+                        raise EmailSyntaxError("Extra character(s) found after close quote: "
+                                               + ", ".join(safe_character_display(c) for c in text[i + 1:]))
+                    break
+                else:
+                    value += c
+            elif i == 0 and c == '"':
+                quoted = True
+            else:
+                value += c
+
+        return value, quoted
+
+    # Split the string at the first unquoted @-sign or left angle bracket.
+    left_part, right_part = split_string_at_unquoted_special(email, ("@", "<"))
+
+    # If the right part starts with an angle bracket,
+    # then the left part is a display name and the rest
+    # of the right part up to the final right angle bracket
+    # is the email address, .
+    if right_part.startswith("<"):
+        # Remove space between the display name and angle bracket.
+        left_part = left_part.rstrip()
+
+        # Unquote and unescape the display name.
+        display_name, display_name_quoted = unquote_quoted_string(left_part)
+
+        # Check that only basic characters are present in a
+        # non-quoted display name.
+        if not display_name_quoted:
+            bad_chars = {
+                safe_character_display(c)
+                for c in display_name
+                if (not ATEXT_RE.match(c) and c != ' ') or c == '.'
+            }
+            if bad_chars:
+                raise EmailSyntaxError("The display name contains invalid characters when not quoted: " + ", ".join(sorted(bad_chars)) + ".")
+
+        # Check for other unsafe characters.
+        check_unsafe_chars(display_name, allow_space=True)
+
+        # Check that the right part ends with an angle bracket
+        # but allow spaces after it, I guess.
+        if ">" not in right_part:
+            raise EmailSyntaxError("An open angle bracket at the start of the email address has to be followed by a close angle bracket at the end.")
+        right_part = right_part.rstrip(" ")
+        if right_part[-1] != ">":
+            raise EmailSyntaxError("There can't be anything after the email address.")
+
+        # Remove the initial and trailing angle brackets.
+        addr_spec = right_part[1:].rstrip(">")
+
+        # Split the email address at the first unquoted @-sign.
+        local_part, domain_part = split_string_at_unquoted_special(addr_spec, ("@",))
+
+    # Otherwise there is no display name. The left part is the local
+    # part and the right part is the domain.
+    else:
+        display_name = None
+        local_part, domain_part = left_part, right_part
+
+    if domain_part.startswith("@"):
+        domain_part = domain_part[1:]
+
+    # Unquote the local part if it is quoted.
+    local_part, is_quoted_local_part = unquote_quoted_string(local_part)
+
+    return display_name, local_part, domain_part, is_quoted_local_part
+
+
+def get_length_reason(addr: str, limit: int) -> str:
+    """Helper function to return an error message related to invalid length."""
+    diff = len(addr) - limit
+    suffix = "s" if diff > 1 else ""
+    return f"({diff} character{suffix} too many)"
+
+
+def safe_character_display(c: str) -> str:
+    # Return safely displayable characters in quotes.
+    if c == '\\':
+        return f"\"{c}\""  # can't use repr because it escapes it
+    if unicodedata.category(c)[0] in ("L", "N", "P", "S"):
+        return repr(c)
+
+    # Construct a hex string in case the unicode name doesn't exist.
+    if ord(c) < 0xFFFF:
+        h = f"U+{ord(c):04x}".upper()
+    else:
+        h = f"U+{ord(c):08x}".upper()
+
+    # Return the character name or, if it has no name, the hex string.
+    return unicodedata.name(c, h)
+
+
+class LocalPartValidationResult(TypedDict):
+    local_part: str
+    ascii_local_part: Optional[str]
+    smtputf8: bool
+
+
+def validate_email_local_part(local: str, allow_smtputf8: bool = True, allow_empty_local: bool = False,
+                              quoted_local_part: bool = False) -> LocalPartValidationResult:
+    """Validates the syntax of the local part of an email address."""
+
+    if len(local) == 0:
+        if not allow_empty_local:
+            raise EmailSyntaxError("There must be something before the @-sign.")
+
+        # The caller allows an empty local part. Useful for validating certain
+        # Postfix aliases.
+        return {
+            "local_part": local,
+            "ascii_local_part": local,
+            "smtputf8": False,
+        }
+
+    # Check the length of the local part by counting characters.
+    # (RFC 5321 4.5.3.1.1)
+    # We're checking the number of characters here. If the local part
+    # is ASCII-only, then that's the same as bytes (octets). If it's
+    # internationalized, then the UTF-8 encoding may be longer, but
+    # that may not be relevant. We will check the total address length
+    # instead.
+    if len(local) > LOCAL_PART_MAX_LENGTH:
+        reason = get_length_reason(local, limit=LOCAL_PART_MAX_LENGTH)
+        raise EmailSyntaxError(f"The email address is too long before the @-sign {reason}.")
+
+    # Check the local part against the non-internationalized regular expression.
+    # Most email addresses match this regex so it's probably fastest to check this first.
+    # (RFC 5322 3.2.3)
+    # All local parts matching the dot-atom rule are also valid as a quoted string
+    # so if it was originally quoted (quoted_local_part is True) and this regex matches,
+    # it's ok.
+    # (RFC 5321 4.1.2 / RFC 5322 3.2.4).
+    if DOT_ATOM_TEXT.match(local):
+        # It's valid. And since it's just the permitted ASCII characters,
+        # it's normalized and safe. If the local part was originally quoted,
+        # the quoting was unnecessary and it'll be returned as normalized to
+        # non-quoted form.
+
+        # Return the local part and flag that SMTPUTF8 is not needed.
+        return {
+            "local_part": local,
+            "ascii_local_part": local,
+            "smtputf8": False,
+        }
+
+    # The local part failed the basic dot-atom check. Try the extended character set
+    # for internationalized addresses. It's the same pattern but with additional
+    # characters permitted.
+    # RFC 6531 section 3.3.
+    valid: Optional[str] = None
+    requires_smtputf8 = False
+    if DOT_ATOM_TEXT_INTL.match(local):
+        # But international characters in the local part may not be permitted.
+        if not allow_smtputf8:
+            # Check for invalid characters against the non-internationalized
+            # permitted character set.
+            # (RFC 5322 3.2.3)
+            bad_chars = {
+                safe_character_display(c)
+                for c in local
+                if not ATEXT_RE.match(c)
+            }
+            if bad_chars:
+                raise EmailSyntaxError("Internationalized characters before the @-sign are not supported: " + ", ".join(sorted(bad_chars)) + ".")
+
+            # Although the check above should always find something, fall back to this just in case.
+            raise EmailSyntaxError("Internationalized characters before the @-sign are not supported.")
+
+        # It's valid.
+        valid = "dot-atom"
+        requires_smtputf8 = True
+
+    # There are no syntactic restrictions on quoted local parts, so if
+    # it was originally quoted, it is probably valid. More characters
+    # are allowed, like @-signs, spaces, and quotes, and there are no
+    # restrictions on the placement of dots, as in dot-atom local parts.
+    elif quoted_local_part:
+        # Check for invalid characters in a quoted string local part.
+        # (RFC 5321 4.1.2. RFC 5322 lists additional permitted *obsolete*
+        # characters which are *not* allowed here. RFC 6531 section 3.3
+        # extends the range to UTF8 strings.)
+        bad_chars = {
+            safe_character_display(c)
+            for c in local
+            if not QTEXT_INTL.match(c)
+        }
+        if bad_chars:
+            raise EmailSyntaxError("The email address contains invalid characters in quotes before the @-sign: " + ", ".join(sorted(bad_chars)) + ".")
+
+        # See if any characters are outside of the ASCII range.
+        bad_chars = {
+            safe_character_display(c)
+            for c in local
+            if not (32 <= ord(c) <= 126)
+        }
+        if bad_chars:
+            requires_smtputf8 = True
+
+            # International characters in the local part may not be permitted.
+            if not allow_smtputf8:
+                raise EmailSyntaxError("Internationalized characters before the @-sign are not supported: " + ", ".join(sorted(bad_chars)) + ".")
+
+        # It's valid.
+        valid = "quoted"
+
+    # If the local part matches the internationalized dot-atom form or was quoted,
+    # perform additional checks for Unicode strings.
+    if valid:
+        # Check that the local part is a valid, safe, and sensible Unicode string.
+        # Some of this may be redundant with the range U+0080 to U+10FFFF that is checked
+        # by DOT_ATOM_TEXT_INTL and QTEXT_INTL. Other characters may be permitted by the
+        # email specs, but they may not be valid, safe, or sensible Unicode strings.
+        # See the function for rationale.
+        check_unsafe_chars(local, allow_space=(valid == "quoted"))
+
+        # Try encoding to UTF-8. Failure is possible with some characters like
+        # surrogate code points, but those are checked above. Still, we don't
+        # want to have an unhandled exception later.
+        try:
+            local.encode("utf8")
+        except ValueError as e:
+            raise EmailSyntaxError("The email address contains an invalid character.") from e
+
+        # If this address passes only by the quoted string form, re-quote it
+        # and backslash-escape quotes and backslashes (removing any unnecessary
+        # escapes). Per RFC 5321 4.1.2, "all quoted forms MUST be treated as equivalent,
+        # and the sending system SHOULD transmit the form that uses the minimum quoting possible."
+        if valid == "quoted":
+            local = '"' + re.sub(r'(["\\])', r'\\\1', local) + '"'
+
+        return {
+            "local_part": local,
+            "ascii_local_part": local if not requires_smtputf8 else None,
+            "smtputf8": requires_smtputf8,
+        }
+
+    # It's not a valid local part. Let's find out why.
+    # (Since quoted local parts are all valid or handled above, these checks
+    # don't apply in those cases.)
+
+    # Check for invalid characters.
+    # (RFC 5322 3.2.3, plus RFC 6531 3.3)
+    bad_chars = {
+        safe_character_display(c)
+        for c in local
+        if not ATEXT_INTL_DOT_RE.match(c)
+    }
+    if bad_chars:
+        raise EmailSyntaxError("The email address contains invalid characters before the @-sign: " + ", ".join(sorted(bad_chars)) + ".")
+
+    # Check for dot errors imposted by the dot-atom rule.
+    # (RFC 5322 3.2.3)
+    check_dot_atom(local, 'An email address cannot start with a {}.', 'An email address cannot have a {} immediately before the @-sign.', is_hostname=False)
+
+    # All of the reasons should already have been checked, but just in case
+    # we have a fallback message.
+    raise EmailSyntaxError("The email address contains invalid characters before the @-sign.")
+
+
+def check_unsafe_chars(s: str, allow_space: bool = False) -> None:
+    # Check for unsafe characters or characters that would make the string
+    # invalid or non-sensible Unicode.
+    bad_chars = set()
+    for i, c in enumerate(s):
+        category = unicodedata.category(c)
+        if category[0] in ("L", "N", "P", "S"):
+            # Letters, numbers, punctuation, and symbols are permitted.
+            pass
+        elif category[0] == "M":
+            # Combining character in first position would combine with something
+            # outside of the email address if concatenated, so they are not safe.
+            # We also check if this occurs after the @-sign, which would not be
+            # sensible because it would modify the @-sign.
+            if i == 0:
+                bad_chars.add(c)
+        elif category == "Zs":
+            # Spaces outside of the ASCII range are not specifically disallowed in
+            # internationalized addresses as far as I can tell, but they violate
+            # the spirit of the non-internationalized specification that email
+            # addresses do not contain ASCII spaces when not quoted. Excluding
+            # ASCII spaces when not quoted is handled directly by the atom regex.
+            #
+            # In quoted-string local parts, spaces are explicitly permitted, and
+            # the ASCII space has category Zs, so we must allow it here, and we'll
+            # allow all Unicode spaces to be consistent.
+            if not allow_space:
+                bad_chars.add(c)
+        elif category[0] == "Z":
+            # The two line and paragraph separator characters (in categories Zl and Zp)
+            # are not specifically disallowed in internationalized addresses
+            # as far as I can tell, but they violate the spirit of the non-internationalized
+            # specification that email addresses do not contain line breaks when not quoted.
+            bad_chars.add(c)
+        elif category[0] == "C":
+            # Control, format, surrogate, private use, and unassigned code points (C)
+            # are all unsafe in various ways. Control and format characters can affect
+            # text rendering if the email address is concatenated with other text.
+            # Bidirectional format characters are unsafe, even if used properly, because
+            # they cause an email address to render as a different email address.
+            # Private use characters do not make sense for publicly deliverable
+            # email addresses.
+            bad_chars.add(c)
+        else:
+            # All categories should be handled above, but in case there is something new
+            # to the Unicode specification in the future, reject all other categories.
+            bad_chars.add(c)
+    if bad_chars:
+        raise EmailSyntaxError("The email address contains unsafe characters: "
+                               + ", ".join(safe_character_display(c) for c in sorted(bad_chars)) + ".")
+
+
+def check_dot_atom(label: str, start_descr: str, end_descr: str, is_hostname: bool) -> None:
+    # RFC 5322 3.2.3
+    if label.endswith("."):
+        raise EmailSyntaxError(end_descr.format("period"))
+    if label.startswith("."):
+        raise EmailSyntaxError(start_descr.format("period"))
+    if ".." in label:
+        raise EmailSyntaxError("An email address cannot have two periods in a row.")
+
+    if is_hostname:
+        # RFC 952
+        if label.endswith("-"):
+            raise EmailSyntaxError(end_descr.format("hyphen"))
+        if label.startswith("-"):
+            raise EmailSyntaxError(start_descr.format("hyphen"))
+        if ".-" in label or "-." in label:
+            raise EmailSyntaxError("An email address cannot have a period and a hyphen next to each other.")
+
+
+class DomainNameValidationResult(TypedDict):
+    ascii_domain: str
+    domain: str
+
+
+def validate_email_domain_name(domain: str, test_environment: bool = False, globally_deliverable: bool = True) -> DomainNameValidationResult:
+    """Validates the syntax of the domain part of an email address."""
+
+    # Check for invalid characters.
+    # (RFC 952 plus RFC 6531 section 3.3 for internationalized addresses)
+    bad_chars = {
+        safe_character_display(c)
+        for c in domain
+        if not ATEXT_HOSTNAME_INTL.match(c)
+    }
+    if bad_chars:
+        raise EmailSyntaxError("The part after the @-sign contains invalid characters: " + ", ".join(sorted(bad_chars)) + ".")
+
+    # Check for unsafe characters.
+    # Some of this may be redundant with the range U+0080 to U+10FFFF that is checked
+    # by DOT_ATOM_TEXT_INTL. Other characters may be permitted by the email specs, but
+    # they may not be valid, safe, or sensible Unicode strings.
+    check_unsafe_chars(domain)
+
+    # Perform UTS-46 normalization, which includes casefolding, NFC normalization,
+    # and converting all label separators (the period/full stop, fullwidth full stop,
+    # ideographic full stop, and halfwidth ideographic full stop) to regular dots.
+    # It will also raise an exception if there is an invalid character in the input,
+    # such as "⒈" which is invalid because it would expand to include a dot and
+    # U+1FEF which normalizes to a backtick, which is not an allowed hostname character.
+    # Since several characters *are* normalized to a dot, this has to come before
+    # checks related to dots, like check_dot_atom which comes next.
+    original_domain = domain
+    try:
+        domain = idna.uts46_remap(domain, std3_rules=False, transitional=False)
+    except idna.IDNAError as e:
+        raise EmailSyntaxError(f"The part after the @-sign contains invalid characters ({e}).") from e
+
+    # Check for invalid characters after Unicode normalization which are not caught
+    # by uts46_remap (see tests for examples).
+    bad_chars = {
+        safe_character_display(c)
+        for c in domain
+        if not ATEXT_HOSTNAME_INTL.match(c)
+    }
+    if bad_chars:
+        raise EmailSyntaxError("The part after the @-sign contains invalid characters after Unicode normalization: " + ", ".join(sorted(bad_chars)) + ".")
+
+    # The domain part is made up dot-separated "labels." Each label must
+    # have at least one character and cannot start or end with dashes, which
+    # means there are some surprising restrictions on periods and dashes.
+    # Check that before we do IDNA encoding because the IDNA library gives
+    # unfriendly errors for these cases, but after UTS-46 normalization because
+    # it can insert periods and hyphens (from fullwidth characters).
+    # (RFC 952, RFC 1123 2.1, RFC 5322 3.2.3)
+    check_dot_atom(domain, 'An email address cannot have a {} immediately after the @-sign.', 'An email address cannot end with a {}.', is_hostname=True)
+
+    # Check for RFC 5890's invalid R-LDH labels, which are labels that start
+    # with two characters other than "xn" and two dashes.
+    for label in domain.split("."):
+        if re.match(r"(?!xn)..--", label, re.I):
+            raise EmailSyntaxError("An email address cannot have two letters followed by two dashes immediately after the @-sign or after a period, except Punycode.")
+
+    if DOT_ATOM_TEXT_HOSTNAME.match(domain):
+        # This is a valid non-internationalized domain.
+        ascii_domain = domain
+    else:
+        # If international characters are present in the domain name, convert
+        # the domain to IDNA ASCII. If internationalized characters are present,
+        # the MTA must either support SMTPUTF8 or the mail client must convert the
+        # domain name to IDNA before submission.
+        #
+        # For ASCII-only domains, the transformation does nothing and is safe to
+        # apply. However, to ensure we don't rely on the idna library for basic
+        # syntax checks, we don't use it if it's not needed.
+        #
+        # idna.encode also checks the domain name length after encoding but it
+        # doesn't give a nice error, so we call the underlying idna.alabel method
+        # directly. idna.alabel checks label length and doesn't give great messages,
+        # but we can't easily go to lower level methods.
+        try:
+            ascii_domain = ".".join(
+                idna.alabel(label).decode("ascii")
+                for label in domain.split(".")
+            )
+        except idna.IDNAError as e:
+            # Some errors would have already been raised by idna.uts46_remap.
+            raise EmailSyntaxError(f"The part after the @-sign is invalid ({e}).") from e
+
+        # Check the syntax of the string returned by idna.encode.
+        # It should never fail.
+        if not DOT_ATOM_TEXT_HOSTNAME.match(ascii_domain):
+            raise EmailSyntaxError("The email address contains invalid characters after the @-sign after IDNA encoding.")
+
+    # Check the length of the domain name in bytes.
+    # (RFC 1035 2.3.4 and RFC 5321 4.5.3.1.2)
+    # We're checking the number of bytes ("octets") here, which can be much
+    # higher than the number of characters in internationalized domains,
+    # on the assumption that the domain may be transmitted without SMTPUTF8
+    # as IDNA ASCII. (This is also checked by idna.encode, so this exception
+    # is never reached for internationalized domains.)
+    if len(ascii_domain) > DOMAIN_MAX_LENGTH:
+        if ascii_domain == original_domain:
+            reason = get_length_reason(ascii_domain, limit=DOMAIN_MAX_LENGTH)
+            raise EmailSyntaxError(f"The email address is too long after the @-sign {reason}.")
+        else:
+            diff = len(ascii_domain) - DOMAIN_MAX_LENGTH
+            s = "" if diff == 1 else "s"
+            raise EmailSyntaxError(f"The email address is too long after the @-sign ({diff} byte{s} too many after IDNA encoding).")
+
+    # Also check the label length limit.
+    # (RFC 1035 2.3.1)
+    for label in ascii_domain.split("."):
+        if len(label) > DNS_LABEL_LENGTH_LIMIT:
+            reason = get_length_reason(label, limit=DNS_LABEL_LENGTH_LIMIT)
+            raise EmailSyntaxError(f"After the @-sign, periods cannot be separated by so many characters {reason}.")
+
+    if globally_deliverable:
+        # All publicly deliverable addresses have domain names with at least
+        # one period, at least for gTLDs created since 2013 (per the ICANN Board
+        # New gTLD Program Committee, https://www.icann.org/en/announcements/details/new-gtld-dotless-domain-names-prohibited-30-8-2013-en).
+        # We'll consider the lack of a period a syntax error
+        # since that will match people's sense of what an email address looks
+        # like. We'll skip this in test environments to allow '@test' email
+        # addresses.
+        if "." not in ascii_domain and not (ascii_domain == "test" and test_environment):
+            raise EmailSyntaxError("The part after the @-sign is not valid. It should have a period.")
+
+        # We also know that all TLDs currently end with a letter.
+        if not DOMAIN_NAME_REGEX.search(ascii_domain):
+            raise EmailSyntaxError("The part after the @-sign is not valid. It is not within a valid top-level domain.")
+
+    # Check special-use and reserved domain names.
+    # Some might fail DNS-based deliverability checks, but that
+    # can be turned off, so we should fail them all sooner.
+    # See the references in __init__.py.
+    from . import SPECIAL_USE_DOMAIN_NAMES
+    for d in SPECIAL_USE_DOMAIN_NAMES:
+        # See the note near the definition of SPECIAL_USE_DOMAIN_NAMES.
+        if d == "test" and test_environment:
+            continue
+
+        if ascii_domain == d or ascii_domain.endswith("." + d):
+            raise EmailSyntaxError("The part after the @-sign is a special-use or reserved name that cannot be used with email.")
+
+    # We may have been given an IDNA ASCII domain to begin with. Check
+    # that the domain actually conforms to IDNA. It could look like IDNA
+    # but not be actual IDNA. For ASCII-only domains, the conversion out
+    # of IDNA just gives the same thing back.
+    #
+    # This gives us the canonical internationalized form of the domain,
+    # which we return to the caller as a part of the normalized email
+    # address.
+    try:
+        domain_i18n = idna.decode(ascii_domain.encode('ascii'))
+    except idna.IDNAError as e:
+        raise EmailSyntaxError(f"The part after the @-sign is not valid IDNA ({e}).") from e
+
+    # Check that this normalized domain name has not somehow become
+    # an invalid domain name. All of the checks before this point
+    # using the idna package probably guarantee that we now have
+    # a valid international domain name in most respects. But it
+    # doesn't hurt to re-apply some tests to be sure. See the similar
+    # tests above.
+
+    # Check for invalid and unsafe characters. We have no test
+    # case for this.
+    bad_chars = {
+        safe_character_display(c)
+        for c in domain
+        if not ATEXT_HOSTNAME_INTL.match(c)
+    }
+    if bad_chars:
+        raise EmailSyntaxError("The part after the @-sign contains invalid characters: " + ", ".join(sorted(bad_chars)) + ".")
+    check_unsafe_chars(domain)
+
+    # Check that it can be encoded back to IDNA ASCII. We have no test
+    # case for this.
+    try:
+        idna.encode(domain_i18n)
+    except idna.IDNAError as e:
+        raise EmailSyntaxError(f"The part after the @-sign became invalid after normalizing to international characters ({e}).") from e
+
+    # Return the IDNA ASCII-encoded form of the domain, which is how it
+    # would be transmitted on the wire (except when used with SMTPUTF8
+    # possibly), as well as the canonical Unicode form of the domain,
+    # which is better for display purposes. This should also take care
+    # of RFC 6532 section 3.1's suggestion to apply Unicode NFC
+    # normalization to addresses.
+    return {
+        "ascii_domain": ascii_domain,
+        "domain": domain_i18n,
+    }
+
+
+def validate_email_length(addrinfo: ValidatedEmail) -> None:
+    # There are three forms of the email address whose length must be checked:
+    #
+    # 1) The original email address string. Since callers may continue to use
+    #    this string, even though we recommend using the normalized form, we
+    #    should not pass validation when the original input is not valid. This
+    #    form is checked first because it is the original input.
+    # 2) The normalized email address. We perform Unicode NFC normalization of
+    #    the local part, we normalize the domain to internationalized characters
+    #    (if originaly IDNA ASCII) which also includes Unicode normalization,
+    #    and we may remove quotes in quoted local parts. We recommend that
+    #    callers use this string, so it must be valid.
+    # 3) The email address with the IDNA ASCII representation of the domain
+    #    name, since this string may be used with email stacks that don't
+    #    support UTF-8. Since this is the least likely to be used by callers,
+    #    it is checked last. Note that ascii_email will only be set if the
+    #    local part is ASCII, but conceivably the caller may combine a
+    #    internationalized local part with an ASCII domain, so we check this
+    #    on that combination also. Since we only return the normalized local
+    #    part, we use that (and not the unnormalized local part).
+    #
+    # In all cases, the length is checked in UTF-8 because the SMTPUTF8
+    # extension to SMTP validates the length in bytes.
+
+    addresses_to_check = [
+        (addrinfo.original, None),
+        (addrinfo.normalized, "after normalization"),
+        ((addrinfo.ascii_local_part or addrinfo.local_part or "") + "@" + addrinfo.ascii_domain, "when the part after the @-sign is converted to IDNA ASCII"),
+    ]
+
+    for addr, reason in addresses_to_check:
+        addr_len = len(addr)
+        addr_utf8_len = len(addr.encode("utf8"))
+        diff = addr_utf8_len - EMAIL_MAX_LENGTH
+        if diff > 0:
+            if reason is None and addr_len == addr_utf8_len:
+                # If there is no normalization or transcoding,
+                # we can give a simple count of the number of
+                # characters over the limit.
+                reason = get_length_reason(addr, limit=EMAIL_MAX_LENGTH)
+            elif reason is None:
+                # If there is no normalization but there is
+                # some transcoding to UTF-8, we can compute
+                # the minimum number of characters over the
+                # limit by dividing the number of bytes over
+                # the limit by the maximum number of bytes
+                # per character.
+                mbpc = max(len(c.encode("utf8")) for c in addr)
+                mchars = max(1, diff // mbpc)
+                suffix = "s" if diff > 1 else ""
+                if mchars == diff:
+                    reason = f"({diff} character{suffix} too many)"
+                else:
+                    reason = f"({mchars}-{diff} character{suffix} too many)"
+            else:
+                # Since there is normalization, the number of
+                # characters in the input that need to change is
+                # impossible to know.
+                suffix = "s" if diff > 1 else ""
+                reason += f" ({diff} byte{suffix} too many)"
+            raise EmailSyntaxError(f"The email address is too long {reason}.")
+
+
+class DomainLiteralValidationResult(TypedDict):
+    domain_address: Union[ipaddress.IPv4Address, ipaddress.IPv6Address]
+    domain: str
+
+
+def validate_email_domain_literal(domain_literal: str) -> DomainLiteralValidationResult:
+    # This is obscure domain-literal syntax. Parse it and return
+    # a compressed/normalized address.
+    # RFC 5321 4.1.3 and RFC 5322 3.4.1.
+
+    addr: Union[ipaddress.IPv4Address, ipaddress.IPv6Address]
+
+    # Try to parse the domain literal as an IPv4 address.
+    # There is no tag for IPv4 addresses, so we can never
+    # be sure if the user intends an IPv4 address.
+    if re.match(r"^[0-9\.]+$", domain_literal):
+        try:
+            addr = ipaddress.IPv4Address(domain_literal)
+        except ValueError as e:
+            raise EmailSyntaxError(f"The address in brackets after the @-sign is not valid: It is not an IPv4 address ({e}) or is missing an address literal tag.") from e
+
+        # Return the IPv4Address object and the domain back unchanged.
+        return {
+            "domain_address": addr,
+            "domain": f"[{addr}]",
+        }
+
+    # If it begins with "IPv6:" it's an IPv6 address.
+    if domain_literal.startswith("IPv6:"):
+        try:
+            addr = ipaddress.IPv6Address(domain_literal[5:])
+        except ValueError as e:
+            raise EmailSyntaxError(f"The IPv6 address in brackets after the @-sign is not valid ({e}).") from e
+
+        # Return the IPv6Address object and construct a normalized
+        # domain literal.
+        return {
+            "domain_address": addr,
+            "domain": f"[IPv6:{addr.compressed}]",
+        }
+
+    # Nothing else is valid.
+
+    if ":" not in domain_literal:
+        raise EmailSyntaxError("The part after the @-sign in brackets is not an IPv4 address and has no address literal tag.")
+
+    # The tag (the part before the colon) has character restrictions,
+    # but since it must come from a registry of tags (in which only "IPv6" is defined),
+    # there's no need to check the syntax of the tag. See RFC 5321 4.1.2.
+
+    # Check for permitted ASCII characters. This actually doesn't matter
+    # since there will be an exception after anyway.
+    bad_chars = {
+        safe_character_display(c)
+        for c in domain_literal
+        if not DOMAIN_LITERAL_CHARS.match(c)
+    }
+    if bad_chars:
+        raise EmailSyntaxError("The part after the @-sign contains invalid characters in brackets: " + ", ".join(sorted(bad_chars)) + ".")
+
+    # There are no other domain literal tags.
+    # https://www.iana.org/assignments/address-literal-tags/address-literal-tags.xhtml
+    raise EmailSyntaxError("The part after the @-sign contains an invalid address literal tag in brackets.")