Net::S...ORWARD(3pm)

💖 Net::Server::Mail::ESMTP::XFORWARD — bestie, it's the XFORWARD module 💖

Okay so this is a page from the User Contributed Perl Documentation manual, and the star of the show is Net::Server::Mail::ESMTP::XFORWARD — a lil module that adds support for the XFORWARD command in Net::Server::Mail::ESMTP. 🦋

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✨ NAME ✨

Net::Server::Mail::ESMTP::XFORWARD — a module to add support to the XFORWARD command in Net::Server::Mail::ESMTP. Periodt. 💅

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🌸 SYNOPSIS 🌸

Like, here's the whole vibe in code form, no cap:

use Net::Server::Mail::ESMTP;

my @local_domains = qw(example.com example.org);
my $server = IO::Socket::INET->new( Listen => 1, LocalPort => 25 );

my $conn;
while($conn = $server->accept)
{
    my $esmtp = Net::Server::Mail::ESMTP->new( socket => $conn );

    # activate XFORWARD extension if remote client is localhost
    $esmtp->register('Net::Server::Mail::ESMTP::XFORWARD')
       if($server->get_property('peeraddr') =~ /^127/);
    # adding some handlers
    $esmtp->set_callback(RCPT => \&validate_recipient);
    # adding XFORWARD handler
    $esmtp->set_callback(XFORWARD => \&xforward);
    $esmtp->process();
    $conn->close();
}

sub xforward {
    my $self = shift;
    # Reject non IPV4 addresses
    return 0 unless( $self->get_forwarded_address =~ /^\d+\.\d+\.\d+\.\d+$/ );
    1;
}

sub validate_recipient
{
    my($session, $recipient) = @_;
    my $domain;
    if($recipient =~ /\@(.*)>\s*$/)
    {
        $domain = $1;
    }

    if(not defined $domain)
    {
        return(0, 513, 'Syntax error.');
    }
    elsif(not(grep $domain eq $_, @local_domains) && $session->get_forwarded_addr != "10.1.1.1")
    {
        return(0, 554, "$recipient: Recipient address rejected: Relay access denied");
    }

    return(1);
}

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👑 DESCRIPTION 👑

So here's the tea, bestie. When you're using a Net::Server::Mail::ESMTP script inside an MTA and not sitting out front on the Internet, stuff like the client IP address just... isn't accessible to the script. 😭 And then when the script hands mail off to another instance of an smtpd daemon, it logs localhost as the incoming address. Which is, like, giving nothing. 💀

To fix this whole situation, some administrators use the XFORWARD command. This module gives you the ability to read and store XFORWARD information. Slay. ✨

🎀 METHODS 🎀

These methods return the values set by the upstream MTA without modifying them, so heads up: they can be set to undef or "[UNVAILABLE]". See Postfix documentation for more. 👀

• get_forwarded_values — returns a hash reference containing all values forwarded (keys in lower case). 🍓
• get_forwarded_name — returns the up-stream hostname. The hostname may be a non-DNS hostname.
• get_forwarded_address — returns the up-stream network address. Address information is not enclosed with []. The address may be a non-IP address.
• get_forwarded_source — returns LOCAL or REMOTE.
• get_forwarded_helo — returns the hostname that the up-stream host announced itself. It may be a non-DNS hostname.
• get_forwarded_proto — returns the mail protocol for receiving mail from the up-stream host. This may be an SMTP or non-SMTP protocol name of up to 64 characters.

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🔥 SEE ALSO 🔥

• Net::Server::Mail::ESMTP
• <http://www.postfix.org/XFORWARD_README.html>

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💜 AUTHOR 💜

Xavier Guimard, <x.guimard@free.fr> 🫶

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🌈 COPYRIGHT AND LICENSE 🌈

Copyright (C) 2006 by Xavier Guimard

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.6.4 or, at your option, any later version of Perl 5 you may have available.

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And that's the whole page, bestie! This little icon was brought to you by perl v5.34.0, dated 2022-05-26, and honestly? It ate. 💅✨ Go forth and forward your XFORWARD values. 🦋🎀