Author image Kevin A. McGrail
and 1 contributors


Net::validMX - PERL Module to use DNS and/or regular expressions to verify if an email address could be valid.


Net::validMX - I wanted the ability to use DNS to verify if an email address COULD be valid by checking for valid MX records. This could be used for sender verification for emails with a program such as MIMEDefang or for websites to verify email addresses prior to registering users and/or sending a confirmation email.


Net::DNS v0.53 or greater. Test::More.


To install this package, uncompress the distribution, change to the directory where the files are present and type:

        perl Makefile.PL
        make test
        make install


To use the module in your programs you will use the line:

        use Net::validMX;


To check if an email address could be valid by checking the DNS, call the function check_valid_mx with a single email address as the only argument:

        ($rv, $reason) = &Net::validMX::check_valid_mx('');

check_valid_mx will return a true/false integer as the first value and a descriptive text message as warranted.

NOTE: In the event of a DNS resolution problem, we do NOT return a failure. We return a success to prevent DNS outages and delays from producing too many false positives.


To check if an email address is formatted correctly, call the function check_email_validity with a single email address as the only argument:

        $rv = &Net::validMX::check_valid_mx('');

check_email_validity will return a true/false integer where > 0 indicates that the email address looks valid.


To check if an email address is formatted correctly, sanitize the email address some common end-user errors(*) and run check_valid_mx all from a single function, use the function check_email_and_mx with a single email address as the only argument:

        ($rv, $reason, $sanitized_email) = &Net::validMX::check_valid_mx('');

check_email_and_mx will return a true/false integer where > 0 indicates that the email address looks valid, a descriptive text message as warranted, and a sanitized version of the email address argument.

(*) Common end-user errors that are fixed:

All spaces are stripped. Many users seem to enter things like Bob and Carol @ a big
Emails ending in @aol. or @aol are fixed to be Also done for, &


To extract the domain part and local part from an email address, use the function get_domain_from_email with a single email address as the only argument:

        $domain = &Net::validMX::get_domain_from_email('');

get_domain_from_email will return a string with the domain part of the email address argument.

Optionally, you can also receive the local part as well:

        ($local, $domain) = &Net::validMX::get_domain_from_email('');

-head2 check_spf_for_domain

To check if a domain is properly configured to send email, call the function check_spf_for_domain with a domain name as the only argument:

        ($rv, $reason) = &Net::validMX::check_spf_for_domain('');

check_spf_for_domain will return "valid", "suspect", or "bad" as the first value and a descriptive text message as warranted.


The distribution contains an example program to demonstrate working functionality as well to utilize as a command line interface to query one or more email addresses.

Run the program with the space-seperated email addresses to test as your arguments:

        perl example/ 
        perl example/

If you supply only one email address argument, the program will exit with a exit status of 0 for a success and 1 for a failure:

        perl example/ kevin.mcgrail@failed || echo 'This email is no good'     


We are using this routine with MIMEDefang and have been since late 2005 via the filter_sender hooks. For example, make a function that excludes authorized senders for your particular setup and add the following code snippets to your mimedefang-filter:

sub filter_initialize { #for Check Valid MX use Net::validMX qw(check_valid_mx); }

sub is_authorized_sender { my ($sender, $RelayAddr) = @_;

  if ([test for authorized user, private IP's, relay from, etc.]) {
    return 1;
  } else {
    return 0;

sub filter_sender { my ($sender, $ip, $hostname, $helo) = @_; my ($rv, $reason); #md_syslog('warning', "Testing $sender, $ip, $hostname, $helo");

  if (&is_authorized_sender($sender, $RelayAddr)) {
    return ('CONTINUE', "ok");

  if ($sender ne '<>') {
    ($rv, $reason) = &check_valid_mx($sender);
    unless ($rv) {
      md_syslog('warning', "Rejecting $sender - Invalid MX: $reason.");
      return ('REJECT', "Sorry; $sender has an invalid MX record: $reason.");


Copyright (c) 2020 The McGrail Foundation and Kevin A. McGrail. All rights reserved.

This distribution, including all of the files in the Net::validMX package, is free software; you can redistribute it and/or modify it under the Perl Artistic License v1.0 available at



Kevin A. McGrail


v1.0 Released Oct 11, 2005. Original release for MIMEDefang filter.
v2.0 Released Nov 3, 2005. Incorporated many user updates.
v2.1 Released May 23, 2006. Switched to a perl Library (Net::validMX). Small efficiency change to short-circuit the DNS resolution of an IP address.
v2.2 Released May 31, 2006. Clarified the LICENSE by pointing readers to the README. Added functions check_email_and_mx & check_email_validity. Expanded documentation and added check_email_and_mx & check_email_validity calls to example. Cleaned up distribution production. Changed logic to check MX records that resolve to IPs to see if it is privatized first.
v2.3 & 2.4 Unreleased. Clarified the license in the Makefile.PL as artistic rather than perl. Continued documentation cleanup. Submitted for namespace registration with CPAN. Added = to chars for a username in the check_email_validity function. Add test case for Test for DNS where MX1 is private, MX2 is private but MX3 is a valid internet address for a pass. Began adding overloaded parameters to check_valid_mx to add flexibility to override default settings. Added AAAA records as valid for IPv6 support. Rewrote all tests to rely on test points inside a domain we control so that testing passes in the future.
v2.5 Released May 8, 2020. Numerous bug fixes and moved to The McGrail Foundation. This product is in active use in production system.


Releases can be found at and on CPAN at




- I'd like to have the example script automatically built to have the correct #!/usr/bin/perl line and possibly installed in /usr/local/bin.
- I'd like to clean up the pod text so that the code snippets aren't wrapped by pod2text on the README export.
- I'd like to add more IPv6 support including the use of private network addresses (fc00::/7 & fe80:).
- Need to finish the ability to override default variables, procedural and OO methods and complete the documentation.


- I'd like to convert the example script(s) into test script(s).

SOLVED: Test::More was a great way to achieve this!

- I'd like to know more info on what/how to make a META.yml file.

SOLVED: I was using MakeMaker v6.03. Instead I upgraded to 6.30 and make dist or make distdir then created the META.yml file. I also used a trick from Net::DNS' Makefile.PL to add the license, author and abstract data directly to the META.yml file.

- I'd like to make it so that the Makefile.PL creates a README on the fly from the pod in the library instead of pod2text lib/Net/ > README.

SOLVED: Thanks to Andreas J. Koenig for a post he wrote that dealt with my exact problem. I added the PREOP and DIST_DEFAULT to the Makefile.PL. I then modified this to use the same MANIFEST trick that is used for metafile and I'm happy with the end result.


Based on an idea from Les Miksell and much input from Jan Pieter Cornet. Additional thanks to David F. Skoll, Matthew van Eerde, and Mark Damrose for testing and suggestions, plus Bill Cole & Karsten Bräckelmann for code contributions. And sincere apologies in advance if I missed anyone!

5 POD Errors

The following errors were encountered while parsing the POD:

Around line 734:

'=item' outside of any '=over'

Around line 738:

You forgot a '=back' before '=head2'

Around line 866:

You forgot a '=back' before '=head1'

Around line 868:

'=item' outside of any '=over'

Around line 884:

Non-ASCII character seen before =encoding in 'Bräckelmann'. Assuming UTF-8