Check if an email is valid with using SMTP, regexes and blacklists
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py3-validate-email is a package for Python that check if an email is valid, not blacklisted, properly formatted and really exists.

This module is for Python 3.6 and above!


You can install the package with pip:

python -m pip install py3-validate-email


Basic usage:

from validate_email import validate_email
is_valid = validate_email(


email_address: the email address to check

check_format: check whether the email address has a valid structure; defaults to True

check_blacklist: check the email against the blacklist of domains downloaded from; defaults to True

check_dns: check the DNS mx-records, defaults to True

dns_timeout: seconds until DNS timeout; defaults to 10 seconds

check_smtp: check whether the email actually exists by initiating an SMTP conversation; defaults to True

smtp_timeout: seconds until SMTP timeout; defaults to 10 seconds

smtp_helo_host: the hostname to use in SMTP HELO/EHLO; if set to None (the default), the fully qualified domain name of the local host is used

smtp_from_address: the email address used for the sender in the SMTP conversation; if set to None (the default), the email_address parameter is used as the sender as well

smtp_skip_tls: skip the TLS negotiation with the server, even when available. defaults to False

smtp_tls_context: an SSLContext to use with the TLS negotiation when the server supports it. defaults to None

smtp_debug: activate smtplib's debug output which always goes to stderr; defaults to False


The function validate_email() returns the following results:

True All requested checks were successful for the given email address.

False At least one of the requested checks failed for the given email address.

None None of the requested checks failed, but at least one of them yielded an ambiguous result. Currently, the SMTP check is the only check which can actually yield an ambiguous result.

Getting more information

The function validate_email_or_fail() works exactly like validate_email(), except that it raises an exception in the case of validation failure and ambiguous result instead of returning False or None, respectively.

All these exceptions descend from EmailValidationError. Please see below for the exact exceptions raised by the various checks. Note that all exception classes are defined in the module validate_email.exceptions.

Please note that SMTPTemporaryError indicates an ambiguous check result rather than a check failure, so if you use validate_email_or_fail(), you probably want to catch this exception.

The checks

By default, all checks are enabled, but each of them can be disabled by one of the check_... parameters. Note that, however, check_smtp implies check_dns.


Check whether the given email address conforms to the general format requirements of valid email addresses.

validate_email_or_fail() raises AddressFormatError on any failure of this test.


Check whether the domain part of the given email address (the part behind the "@" is known as a disposable and temporary email address domain. These are often used to register dummy users in order to spam or abuse some services.

A list of such domains is maintained at, and this module uses that list.

validate_email_or_fail() raises DomainBlacklistedError if the email address belongs to a blacklisted domain.


Check whether there is a valid list of servers responsible for delivering emails to the given email address.

First, a DNS query is issued for the email address' domain to retrieve a list of all MX records. That list is then stripped of duplicates and malformatted entries. If at the end of this procedure, at least one valid MX record remains, the check is considered successful.

On failure of this check, validate_email_or_fail() raises one of the following exceptions, all of which descend from DNSError:

DomainNotFoundError The domain of the email address cannot be found at all.

NoNameserverError There is no nameserver for the domain.

DNSTimeoutError A timeout occured when querying the nameserver. Note that the timeout period can be changed with the dns_timeout parameter.

DNSConfigurationError The nameserver is misconfigured.

NoMXError The nameserver does not list any MX records for the domain.

NoValidMXError The nameserver lists MX records for the domain, but none of them is valid.


Check whether the given email address exists by simulating an actual email delivery.

A connection to the SMTP server identified through the domain's MX record is established, and an SMTP conversation is initiated up to the point where the server confirms the existence of the email address. After that, instead of actually sending an email, the conversation is cancelled.

Unless you set smtp_skip_tls to True, the module will try to negotiate a TLS connection with STARTTLS, and silently fall back to an unencrypted SMTP connection if the server doesn't support it. Additionally, depending on your client configuration, the TLS negotiation might fail which will result in an ambiguous response for the given host as the module will be unable to communicate with the host after the negotiation fails. In trying to succeed, you can pass an SSLContext as an smtp_tls_context parameter, but remember that the server might still deny the negotiation based on how you set the SSLContext up, and based on its security settings as well.

If the SMTP server replies to the RCPT TO command with a code 250 (success) response, the check is considered successful.

If the SMTP server replies with a code 5xx (permanent error) response at any point in the conversation, the check is considered failed.

If the SMTP server cannot be connected, unexpectedly closes the connection, or replies with a code 4xx (temporary error) at any stage of the conversation, the check is considered ambiguous.

If there is more than one valid MX record for the domain, they are tried in order of priority until the first time the check is either successful or failed. Only in case of an ambiguous check result, the next server is tried, and only if the check result is ambiguous for all servers, the overall check is considered ambiguous as well.

On failure of this check or on ambiguous result, validate_email_or_fail() raises one of the following exceptions, all of which descend from SMTPError:

AddressNotDeliverableError The SMTP server permanently refused the email address. Technically, this means that the server replied to the RCPT TO command with a code 5xx response.

SMTPCommunicationError The SMTP server refused to even let us get to the point where we could ask it about the email address. Technically, this means that the server sent a code 5xx response either immediately after connection, or as a reply to the EHLO (or HELO) or MAIL FROM commands.

SMTPTemporaryError A temporary error occured during the check for all available MX servers. This is considered an ambiguous check result. For example, greylisting is a frequent cause for this. Make sure you check the contents of the message.

All of the above three exceptions provide further details about the error response(s) in the exception's instance variable error_messages.


The package contains an auto-updater for downloading and updating the built-in blacklist.txt. It will run on each module load (and installation), but will try to update the content only if the file is older than 5 days, and if the content is not the same that's already downloaded.

The update can be triggered manually:

from validate_email.updater import update_builtin_blacklist

    force: bool = False,
    background: bool = True,
    callback: Callable = None
) -> Optional[Thread]

force: forces the update even if the downloaded/installed file is fresh enough.

background: starts the update in a Thread so it won't make your code hang while it's updating. If you set this to True, the function will return the Thread used for starting the update so you can join() it if necessary.

callback: An optional Callable (function/method) to be called when the update is done.

You can completely skip the auto-update on startup by setting the environment variable PY3VE_IGNORE_UPDATER to any value.

Read the FAQ!