Awhile back I was noticing I was definitely losing emails. As one can might imagine, this is a scary experience since this brings into doubt if the mail system under use is doing something funny to the mail.
My first place to look was in the mail logs for the SMTP server and other associated daemons. However, I saw nothing in the maillogs which was not a very comforting thought.
After more investigation I would notice empty files like this every once in awhile…
~/Maildir) ls -la new/ total 4 drwx------ 2 al al 512 Jun 8 00:25 . drwx------ 69 al al 2048 Jun 8 00:25 .. -rw------- 1 al al 0 Jun 8 00:22 1244388142.30600_.myserver.net
This gave me more clues on where to look next. So next I looked in my Procmail logs for this particular mail id and noticed the process handling this message was killed by SIGPIPE
procmail: Executing "/usr/local/bin/spamassassin"  warn: spamassassin: killed by SIGPIPE procmail:  Tue Apr 14 21:45:26 2009
Googling dug up the following links that explain it all:
Since I have upgraded Spamassassin, the zero byte email mystery has resolved itself.