<update>

It's really straight forward...

#!/usr/bin/perl -w

use strict;

# $Id: mta.pl,v 0.0 2007/01/19 19:38:39 shmem Exp $

# local delaying MTA

use Carp;
use File::Spec;
use Net::SMTP;
use Net::SMTP::Server;
use Net::SMTP::Server::Client;

my $relay     = 'smarthost';
my $port      = 25;
my $time      = time;
my $spooldir  = 'delayed';
my $maxmsgs   = 30;
my $timeframe = 3600;

-d $spooldir or mkdir $spooldir,0755 or die "spooldir: $!\n";

my $server = new Net::SMTP::Server('localhost', $port) ||
    croak("Unable to handle client connection: $!\n");

my $sentcount = 0;

while(my $conn = $server->accept()) {

    # receive mail and spool it.

    my $client = new Net::SMTP::Server::Client($conn) ||
        croak("Unable to handle client connection: $!\n");

    my $file = File::Spec->catfile($spooldir,time);
    open O, '>', $file or die "Can't write $file: $!\n";

    if ( $client->process ) {
        print O $client->{'FROM'}.$/;
        print O join('|',@{$client->{'TO'}}).$/;
        print O $client->{'MSG'}.$/;
        close O or die "Can't close filehandle O: $!\n";
        warn "[$file] message queued.\n";
    } # else { *shrug*. Client quit. }

    # deliver mails.

    opendir(D, $spooldir) or die "Can't read '$spooldir': $!\n";
    my @files = grep (!/^\.\.?/,readdir D);

    foreach my $file (@files) {
        # reset $sentcount if timeframe passed
        if (time - $time >= $timeframe) {
            $sentcount = 0;
            $time = time;
            warn "timer reset.\n";
        } 

        if ($sentcount == $maxmsgs) {
            warn "Delivery delayed, reached $maxmsgs in $timeframe sec
+s.\n";
            last;
        } 

        my $mailfile = File::Spec->catfile ($spooldir,$file);
        open MAIL, '<', $mailfile
            or die "Can't read '$mailfile': $!\n";

        chomp(my $FROM = <MAIL>);
        chomp(my $TO   = <MAIL>);
        my $MSG        = do { local $/; <MAIL> };
        $TO            = [split /\|/, $TO];
        my $sent       = relay ($FROM, $TO, $MSG);

        if ($sent) {
            $sentcount++;
            unlink $mailfile or die "Can't unlink '$mailfile': $!\n";
            warn "[$file]: (#$sentcount) sent\n";
        } else {
            warn "[$file]: delivery failed \n";
        } 
    } 
} 

sub relay {
    my ($FROM, $TO, $MSG) = @_;
    my $smtp = new Net::SMTP($relay);

    $smtp -> mail ($FROM)  or return;
    $smtp -> to   (@{$TO}) or return;
    $smtp -> data ($MSG)   or return;
    $smtp -> quit          or return;
}
[download]

Eliminating the flaw that mails are only sent after receiving one is left as an excercise to the reader ;-)

</update>

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}