NAME

Mail::Qmail::Filter::CheckDeliverabilty - check deliverability according to .qmail files

SYNOPSIS

    use Mail::Qmail::Filter;
    
    Mail::Qmail::Filter->new->add_filter(
        '::CheckDeliverability' => {
            run_commands_matching => qr{/ezmlm-(?:checksub|reject)\b},
            skip_if_relayclient   => 1,
        },
        '::Queue',
    )->run;

DESCRIPTION

This Mail::Qmail::Filter plugin tries to find the appropriate .qmail file for all envelope recipients and optionally runs commands mentioned in these files to check the deliverability of the message.

Rejects the message if it would be equally undeliverable to all recipients.

For each recipient address, deliverability is checked as follows:

• The appropriate .qmail file is searched using Qmail::Deliverable. If none is found, the address is considered undeliverable, with the "reject_text" as reason.

• Otherwise the .qmail file is evaluated line by line in a similar fashion as qmail-local would:

• Comment lines are skipped.

• When a forward, maildir or mbox line is found, the recipient is considered deliverable, and the filter stops.

• When a command line is found, it is executed only if "run_commands_matching" is set and the line matches the given regular expression.

  When it returns with exit code 100, the filter saves its output as possible reject text, and the evaluation of this .qmail file stops.

• The message is rejected only if the evaluation of each .qmail file resultet with status 100 and the same reject text or if absolutely no valid .qmail files could be found.

NOTE

Please note that it is usually preferable to check deliverability directly after each RCPT TO command within the SMTP transaction, because only then you can reject single recipients individually. To achieve this, you may want to use tools like spamdyke-qrv.

But: These tools do have limitations, e.g. they usually do not call external commands and inherent to the sequence of SMTP commands they cannot take message content into account. And this is where this filters comes in handy.

I use it to reject messages to mailing lists which do not come from a subscriber of these lists. Often these are spam messages with forged sender addresses, and by already rejecting them during the SMTP transaction, one can avoid to produce collateral spam.

OPTIONAL PARAMETERS

run_commands_matching

expects a regular expression as argument against which command lines in the .qmail files are to be matched. Only commands matching this regular expression will be called. You should take care to call only commands which do not deliver the message itself, lest you want to shoot yourself in the foot.

SEE ALSO

"COMMON PARAMETERS FOR ALL FILTERS" in Mail::Qmail::Filter

LICENSE AND COPYRIGHT

Copyright 2019 Martin Sluka.

This module is free software; you can redistribute it and/or modify it under the terms of the the Artistic License (2.0). You may obtain a copy of the full license at:

http://www.perlfoundation.org/artistic_license_2_0

Any use, modification, and distribution of the Standard or Modified Versions is governed by this Artistic License. By using, modifying or distributing the Package, you accept this license. Do not use, modify, or distribute the Package, if you do not accept this license.

If your Modified Version has been derived from a Modified Version made by someone other than you, you are nevertheless required to ensure that your Modified Version complies with the requirements of this license.

This license does not grant you the right to use any trademark, service mark, tradename, or logo of the Copyright Holder.

This license includes the non-exclusive, worldwide, free-of-charge patent license to make, have made, use, offer to sell, sell, import and otherwise transfer the Package with respect to any patent claims licensable by the Copyright Holder that are necessarily infringed by the Package. If you institute patent litigation (including a cross-claim or counterclaim) against any party alleging that the Package constitutes direct or contributory patent infringement, then this Artistic License to you shall terminate on the date that such litigation is filed.

Disclaimer of Warranty: THE PACKAGE IS PROVIDED BY THE COPYRIGHT HOLDER AND CONTRIBUTORS "AS IS' AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES. THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR NON-INFRINGEMENT ARE DISCLAIMED TO THE EXTENT PERMITTED BY YOUR LOCAL LAW. UNLESS REQUIRED BY LAW, NO COPYRIGHT HOLDER OR CONTRIBUTOR WILL BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING IN ANY WAY OUT OF THE USE OF THE PACKAGE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.