maildrop silently discards email - how to troubleshoot?

Hi all,

I am currently seeing a bizarre problem with email delivery, where email sent to a mailman mailing list gets sent back to the poster, gets as far as maildrop, which then causes the mail to silently disappear without a trace.

Focusing on maildroprc, I have the config specified below. The second last step is to log the line "Delivered normally to [path]", and the last step is the "to" command to perform the delivery. Despite logging the second last line correctly, and despite returning an apparent "successful" response back to postfix, the message vanishes completely and no delivery takes place:

Delivered normally to [path]
Date: Thu May 16 07:25:31 2013
From: "Facebook" <[snip]@facebookmail.com>
Subj: [snip]
File: [path]                             (11286)

This problem seems limited only to email sent back to the poster from mailman, it does not affect other mail, which has been working fine on this server for many years.

Normally I would set a verbose debugging mechanism up to get a sense of what maildrop is doing, but verbose logging has no effect when in delivery mode, and I am stuck.

First off, does anyone know why the "to" command would return success without having delivered any email to that directory, and second, does anyone know how to turn on some kind of verbose logging when in delivery mode?

# default logfile
logfile "/var/log/maildrop"
VERBOSE="5"
# Create mailboxes if necessary
`[ -d $HOME/ ]`
if ( $RETURNCODE != 0 )
{
  `maildirmake $HOME`
}
`[ -d $HOME/.Junk/ ]`
if ( $RETURNCODE != 0 )
{
  `maildirmake $HOME/.Junk`
}
`[ -d $HOME/.Trash/ ]`
if ( $RETURNCODE != 0 )
{
   `maildirmake $HOME/.Trash`
}
`[ -d $HOME/.Drafts/ ]`
if ( $RETURNCODE != 0 )
{
   `maildirmake $HOME/.Drafts`
}
# Do not call SA when the sender is in the whitelist.
if (/^From: *!.*/ && lookup(getaddr($MATCH2),"/etc/maildrop/from_whitelist.dat"))
{
   log "Spam: sender found in whitelist"
   to $HOME
}

# Avoid scanning of large emails
#if ( $SIZE < 100000 )
#{
#            # -f -> do not bail out when spamd is down
#            # -u amavis unprivileged account
#        exception {
#                xfilter "/usr/bin/spamc -f -u nobody"
#        }
#}

# Count amount of * to determine where to deliver mail
if (/^X-Spam-Status: Yes, score=[0-9]*.*/)
{
        if ( $MATCH1 > 5 )
         {
         # Log original recipient in /var/vmail/maildrop.log 
         #log "To  : $LOGNAME"
         log "Score more than 5, delivered to $HOME/.Junk/"
         to $HOME/.Junk/
         }
         else
        {
            # Tagged as spam but not exceed the treshhold value of 5
         log "Score less than 5, delivered to $HOME/.Junk/"
         to $HOME/.Junk/
         }
}
else
{
   # Not whitelisted and no spam
log "Delivered normally to $HOME"
to $HOME
}

Two different servers show the exact same symptoms, the versions being used are different on each server, and are as follows:

maildrop-man-2.2.0.20090905-1.5Server
maildrop-2.2.0.20090905-1.5Server
maildrop-devel-2.2.0.20090905-1.5Server

maildrop-devel-2.6.0-1.x86_64
maildrop-2.6.0-1.x86_64

Regards,
Graham
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