email-validator: Validate Email Addresses

A robust email address syntax and deliverability validation library for
Python 3.8+ by Joshua Tauberer.

This library validates that a string is of the form name@example.com
and optionally checks that the domain name is set up to receive email.
This is the sort of validation you would want when you are identifying
users by their email address like on a registration form.

Key features:

Checks that an email address has the correct syntax --- great for
email-based registration/login forms or validing data.
Gives friendly English error messages when validation fails that you
can display to end-users.
Checks deliverability (optional): Does the domain name resolve?
(You can override the default DNS resolver to add query caching.)
Supports internationalized domain names (like @ツ.life),
internationalized local parts (like ツ@example.com),
and optionally parses display names (e.g. "My Name" <me@example.com>).
Rejects addresses with invalid or unsafe Unicode characters,
obsolete email address syntax that you'd find unexpected,
special use domain names like @localhost,
and domains without a dot by default.
This is an opinionated library!
Normalizes email addresses (important for internationalized
and quoted-string addresses! see below).
Python type annotations are used.

This is an opinionated library. You should definitely also consider using
the less-opinionated pyIsEmail
if it works better for you.

View the CHANGELOG / Release Notes for the version history of changes in the library. Occasionally this README is ahead of the latest published package --- see the CHANGELOG for details.

Installation

This package is on PyPI, so:

pip install email-validator

(You might need to use pip3 depending on your local environment.)

Quick Start

If you're validating a user's email address before creating a user
account in your application, you might do this:

from email_validator import validate_email, EmailNotValidError

email = "my+address@example.org"

try:

  # Check that the email address is valid. Turn on check_deliverability
  # for first-time validations like on account creation pages (but not
  # login pages).
  emailinfo = validate_email(email, check_deliverability=False)

  # After this point, use only the normalized form of the email address,
  # especially before going to a database query.
  email = emailinfo.normalized

except EmailNotValidError as e:

  # The exception message is human-readable explanation of why it's
  # not a valid (or deliverable) email address.
  print(str(e))

This validates the address and gives you its normalized form. You should
put the normalized form in your database and always normalize before
checking if an address is in your database. When using this in a login form,
set check_deliverability to False to avoid unnecessary DNS queries.

Usage

Overview

The module provides a function validate_email(email_address) which
takes an email address and:

Raises a EmailNotValidError with a helpful, human-readable error
message explaining why the email address is not valid, or
Returns an object with a normalized form of the email address (which
you should use!) and other information about it.

When an email address is not valid, validate_email raises either an
EmailSyntaxError if the form of the address is invalid or an
EmailUndeliverableError if the domain name fails DNS checks. Both
exception classes are subclasses of EmailNotValidError, which in turn
is a subclass of ValueError.

But when an email address is valid, an object is returned containing
a normalized form of the email address (which you should use!) and
other information.

The validator doesn't, by default, permit obsoleted forms of email addresses
that no one uses anymore even though they are still valid and deliverable, since
they will probably give you grief if you're using email for login. (See
later in the document about how to allow some obsolete forms.)

The validator optionally checks that the domain name in the email address has
a DNS MX record indicating that it can receive email. (Except a Null MX record.
If there is no MX record, a fallback A/AAAA-record is permitted, unless
a reject-all SPF record is present.) DNS is slow and sometimes unavailable or
unreliable, so consider whether these checks are useful for your use case and
turn them off if they aren't.
There is nothing to be gained by trying to actually contact an SMTP server, so
that's not done here. For privacy, security, and practicality reasons, servers
are good at not giving away whether an address is
deliverable or not: email addresses that appear to accept mail at first
can bounce mail after a delay, and bounced mail may indicate a temporary
failure of a good email address (sometimes an intentional failure, like
greylisting).

Options

The validate_email function also accepts the following keyword arguments
(defaults are as shown below):

check_deliverability=True: If true, DNS queries are made to check that the domain name in the email address (the part after the @-sign) can receive mail, as described above. Set to False to skip this DNS-based check. It is recommended to pass False when performing validation for login pages (but not account creation pages) since re-validation of a previously validated domain in your database by querying DNS at every login is probably undesirable. You can also set email_validator.CHECK_DELIVERABILITY to False to turn this off for all calls by default.

dns_resolver=None: Pass an instance of dns.resolver.Resolver to control the DNS resolver including setting a timeout and a cache. The caching_resolver function shown below is a helper function to construct a dns.resolver.Resolver with a LRUCache. Reuse the same resolver instance across calls to validate_email to make use of the cache.

test_environment=False: If True, DNS-based deliverability checks are disabled and test and **.test domain names are permitted (see below). You can also set email_validator.TEST_ENVIRONMENT to True to turn it on for all calls by default.

allow_smtputf8=True: Set to False to prohibit internationalized addresses that would
require the
SMTPUTF8 extension. You can also set email_validator.ALLOW_SMTPUTF8 to False to turn it off for all calls by default.

allow_quoted_local=False: Set to True to allow obscure and potentially problematic email addresses in which the part of the address before the @-sign contains spaces, @-signs, or other surprising characters when the local part is surrounded in quotes (so-called quoted-string local parts). In the object returned by validate_email, the normalized local part removes any unnecessary backslash-escaping and even removes the surrounding quotes if the address would be valid without them. You can also set email_validator.ALLOW_QUOTED_LOCAL to True to turn this on for all calls by default.

allow_domain_literal=False: Set to True to allow bracketed IPv4 and "IPv6:"-prefixd IPv6 addresses in the domain part of the email address. No deliverability checks are performed for these addresses. In the object returned by validate_email, the normalized domain will use the condensed IPv6 format, if applicable. The object's domain_address attribute will hold the parsed ipaddress.IPv4Address or ipaddress.IPv6Address object if applicable. You can also set email_validator.ALLOW_DOMAIN_LITERAL to True to turn this on for all calls by default.

allow_display_name=False: Set to True to allow a display name and bracketed address in the input string, like My Name <me@example.org>. It's implemented in the spirit but not the letter of RFC 5322 3.4, so it may be stricter or more relaxed than what you want. The display name, if present, is provided in the returned object's display_name field after being unquoted and unescaped. You can also set email_validator.ALLOW_DISPLAY_NAME to True to turn this on for all calls by default.

allow_empty_local=False: Set to True to allow an empty local part (i.e.
@example.com), e.g. for validating Postfix aliases.

DNS timeout and cache

When validating many email addresses or to control the timeout (the default is 15 seconds), create a caching dns.resolver.Resolver to reuse in each call. The caching_resolver function returns one easily for you:

from email_validator import validate_email, caching_resolver

resolver = caching_resolver(timeout=10)

while True:
  validate_email(email, dns_resolver=resolver)

Test addresses

This library rejects email addresses that use the Special Use Domain Names invalid, localhost, test, and some others by raising EmailSyntaxError. This is to protect your system from abuse: You probably don't want a user to be able to cause an email to be sent to localhost (although they might be able to still do so via a malicious MX record). However, in your non-production test environments you may want to use @test or @myname.test email addresses. There are three ways you can allow this:

Add test_environment=True to the call to validate_email (see above).
Set email_validator.TEST_ENVIRONMENT to True globally.
Remove the special-use domain name that you want to use from email_validator.SPECIAL_USE_DOMAIN_NAMES, e.g.:

import email_validator
email_validator.SPECIAL_USE_DOMAIN_NAMES.remove("test")

It is tempting to use @example.com/net/org in tests. They are not in this library's SPECIAL_USE_DOMAIN_NAMES list so you can, but shouldn't, use them. These domains are reserved to IANA for use in documentation so there is no risk of accidentally emailing someone at those domains. But beware that this library will nevertheless reject these domain names if DNS-based deliverability checks are not disabled because these domains do not resolve to domains that accept email. In tests, consider using your own domain name or @test or @myname.test instead.

Internationalized email addresses

The email protocol SMTP and the domain name system DNS have historically
only allowed English (ASCII) characters in email addresses and domain names,
respectively. Each has adapted to internationalization in a separate
way, creating two separate aspects to email address internationalization.

(If your mail submission library doesn't support Unicode at all, then
immediately prior to mail submission you must replace the email address with
its ASCII-ized form. This library gives you back the ASCII-ized form in the
ascii_email field in the returned object.)

Internationalized domain names (IDN)

The first is internationalized domain names (RFC
5891), a.k.a IDNA 2008. The DNS
system has not been updated with Unicode support. Instead, internationalized
domain names are converted into a special IDNA ASCII "Punycode"
form starting with xn--. When an email address has non-ASCII
characters in its domain part, the domain part is replaced with its IDNA
ASCII equivalent form in the process of mail transmission. Your mail
submission library probably does this for you transparently. (Compliance
around the web is not very good though.) This library conforms to IDNA 2008
using the idna module by Kim Davies.

Internationalized local parts

The second sort of internationalization is internationalization in the
local part of the address (before the @-sign). In non-internationalized
email addresses, only English letters, numbers, and some punctuation
(._!#$%&'^``*+-=~/?{|}) are allowed. In internationalized email address
local parts, a wider range of Unicode characters are allowed.

Email addresses with these non-ASCII characters require that your mail
submission library and all the mail servers along the route to the destination,
including your own outbound mail server, all support the
SMTPUTF8 (RFC 6531) extension.
Support for SMTPUTF8 varies. If you know ahead of time that SMTPUTF8 is not
supported by your mail submission stack, then you must filter out addresses that
require SMTPUTF8 using the allow_smtputf8=False keyword argument (see above).
This will cause the validation function to raise a EmailSyntaxError if
delivery would require SMTPUTF8. If you do not set allow_smtputf8=False,
you can also check the value of the smtputf8 field in the returned object.

Unsafe Unicode characters are rejected

A surprisingly large number of Unicode characters are not safe to display,
especially when the email address is concatenated with other text, so this
library tries to protect you by not permitting reserved, non-, private use,
formatting (which can be used to alter the display order of characters),
whitespace, and control characters, and combining characters
as the first character of the local part and the domain name (so that they
cannot combine with something outside of the email address string or with
the @-sign). See https://qntm.org/safe and https://trojansource.codes/
for relevant prior work. (Other than whitespace, these are checks that
you should be applying to nearly all user inputs in a security-sensitive
context.) This does not guard against the well known problem that many
Unicode characters look alike, which can be used to fool humans reading
displayed text.

Normalization

Unicode Normalization

The use of Unicode in email addresses introduced a normalization
problem. Different Unicode strings can look identical and have the same
semantic meaning to the user. The normalized field returned on successful
validation provides the correctly normalized form of the given email
address.

For example, the CJK fullwidth Latin letters are considered semantically
equivalent in domain names to their ASCII counterparts. This library
normalizes them to their ASCII counterparts (as required by IDNA):

emailinfo = validate_email("me@Ｄｏｍａｉｎ.com")
print(emailinfo.normalized)
print(emailinfo.ascii_email)
# prints "me@domain.com" twice

Because an end-user might type their email address in different (but
equivalent) un-normalized forms at different times, you ought to
replace what they enter with the normalized form immediately prior to
going into your database (during account creation), querying your database
(during login), or sending outbound mail.

The normalizations include lowercasing the domain part of the email
address (domain names are case-insensitive), Unicode "NFC"
normalization of the
whole address (which turns characters plus combining
characters into
precomposed characters where possible, replacement of fullwidth and
halfwidth
characters
in the domain part, possibly other
UTS46 mappings on the domain part,
and conversion from Punycode to Unicode characters.

Normalization may change the characters in the email address and the
length of the email address, such that a string might be a valid address
before normalization but invalid after, or vice versa. This library only
permits addresses that are valid both before and after normalization.

(See RFC 6532 (internationalized email) section
3.1 and RFC 5895
(IDNA 2008) section 2.)

Other Normalization

Normalization is also applied to quoted-string local parts and domain
literal IPv6 addresses if you have allowed them by the allow_quoted_local
and allow_domain_literal options. In quoted-string local parts, unnecessary
backslash escaping is removed and even the surrounding quotes are removed if
they are unnecessary. For IPv6 domain literals, the IPv6 address is
normalized to condensed form. RFC 2142
also requires lowercase normalization for some specific mailbox names like postmaster@.

Examples

For the email address test@joshdata.me, the returned object is:

ValidatedEmail(
  normalized='test@joshdata.me',
  local_part='test',
  domain='joshdata.me',
  ascii_email='test@joshdata.me',
  ascii_local_part='test',
  ascii_domain='joshdata.me',
  smtputf8=False)

For the fictitious but valid address example@ツ.ⓁⒾⒻⒺ, which has an
internationalized domain but ASCII local part, the returned object is:

ValidatedEmail(
  normalized='example@ツ.life',
  local_part='example',
  domain='ツ.life',
  ascii_email='example@xn--bdk.life',
  ascii_local_part='example',
  ascii_domain='xn--bdk.life',
  smtputf8=False)

Note that normalized and other fields provide a normalized form of the
email address, domain name, and (in other cases) local part (see earlier
discussion of normalization), which you should use in your database.

Calling validate_email with the ASCII form of the above email address,
example@xn--bdk.life, returns the exact same information (i.e., the
normalized field always will contain Unicode characters, not Punycode).

For the fictitious address ツ-test@joshdata.me, which has an
internationalized local part, the returned object is:

ValidatedEmail(
  normalized='ツ-test@joshdata.me',
  local_part='ツ-test',
  domain='joshdata.me',
  ascii_email=None,
  ascii_local_part=None,
  ascii_domain='joshdata.me',
  smtputf8=True)

Now smtputf8 is True and ascii_email is None because the local
part of the address is internationalized. The local_part and normalized fields
return the normalized form of the address.

Return value

When an email address passes validation, the fields in the returned object
are:

Field	Value
`normalized`	The normalized form of the email address that you should put in your database. This combines the `local_part` and `domain` fields (see below).
`ascii_email`	If set, an ASCII-only form of the normalized email address by replacing the domain part with IDNA Punycode. This field will be present when an ASCII-only form of the email address exists (including if the email address is already ASCII). If the local part of the email address contains internationalized characters, `ascii_email` will be `None`. If set, it merely combines `ascii_local_part` and `ascii_domain`.
`local_part`	The normalized local part of the given email address (before the @-sign). Normalization includes Unicode NFC normalization and removing unnecessary quoted-string quotes and backslashes. If `allow_quoted_local` is True and the surrounding quotes are necessary, the quotes will be present in this field.
`ascii_local_part`	If set, the local part, which is composed of ASCII characters only.
`domain`	The canonical internationalized Unicode form of the domain part of the email address. If the returned string contains non-ASCII characters, either the SMTPUTF8 feature of your mail relay will be required to transmit the message or else the email address's domain part must be converted to IDNA ASCII first: Use `ascii_domain` field instead.
`ascii_domain`	The IDNA Punycode-encoded form of the domain part of the given email address, as it would be transmitted on the wire.
`domain_address`	If domain literals are allowed and if the email address contains one, an `ipaddress.IPv4Address` or `ipaddress.IPv6Address` object.
`display_name`	If no display name was present and angle brackets do not surround the address, this 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. If the display name was quoted, it will be unquoted and unescaped.
`smtputf8`	A boolean indicating that the SMTPUTF8 feature of your mail relay will be required to transmit messages to this address because the local part of the address has non-ASCII characters (the local part cannot be IDNA-encoded). If `allow_smtputf8=False` is passed as an argument, this flag will always be false because an exception is raised if it would have been true.
`mx`	A list of (priority, domain) tuples of MX records specified in the DNS for the domain (see RFC 5321 section 5). May be `None` if the deliverability check could not be completed because of a temporary issue like a timeout.
`mx_fallback_type`	`None` if an `MX` record is found. If no MX records are actually specified in DNS and instead are inferred, through an obsolete mechanism, from A or AAAA records, the value is the type of DNS record used instead (`A` or `AAAA`). May be `None` if the deliverability check could not be completed because of a temporary issue like a timeout.
`spf`	Any SPF record found while checking deliverability. Only set if the SPF record is queried.

Assumptions

By design, this validator does not pass all email addresses that
strictly conform to the standards. Many email address forms are obsolete
or likely to cause trouble:

The validator assumes the email address is intended to be
usable on the public Internet. The domain part
of the email address must be a resolvable domain name
(see the deliverability checks described above).
Most Special Use Domain Names
and their subdomains, as well as
domain names without a ., are rejected as a syntax error
(except see the test_environment parameter above).
Obsolete email syntaxes are rejected:
The unusual "(comment)" syntax
is rejected. Extremely old obsolete syntaxes are
rejected. Quoted-string local parts and domain-literal addresses
are rejected by default, but there are options to allow them (see above).
No one uses these forms anymore, and I can't think of any reason why anyone
using this library would need to accept them.

Testing

Tests can be run using

pip install -r test_requirements.txt 
make test

Tests run with mocked DNS responses. When adding or changing tests, temporarily turn on the BUILD_MOCKED_DNS_RESPONSE_DATA flag in tests/mocked_dns_responses.py to re-build the database of mocked responses from live queries.

For Project Maintainers

The package is distributed as a universal wheel and as a source package.

To release:

Update CHANGELOG.md.
Update the version number in email_validator/version.py.
Make & push a commit with the new version number and make sure tests pass.
Make & push a tag (see command below).
Make a release at https://github.com/JoshData/python-email-validator/releases/new.
Publish a source and wheel distribution to pypi (see command below).

git tag v$(cat email_validator/version.py  | sed "s/.* = //" | sed 's/"//g')
git push --tags
./release_to_pypi.sh

License

This project is free of any copyright restrictions per the Unlicense. (Prior to Feb. 4, 2024, the project was made available under the terms of the CC0 1.0 Universal public domain dedication.) See LICENSE and CONTRIBUTING.md.

Dependencies of email-validator (2).
Dependency	Optional
dnspython	false
idna	false

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