Here's an idea: include $HOST as well as $$ in the name of the logfile.
Then
you can't possibly get a conflict.
...., we have many hosts
that handle mail, BUT for a particular user, only ONE host will check that
user's .forward file to call procmail (or whatever).
To clarify, this is the situation where I work, but it has been pointed
out to me that some networks will allow more than one host to share the
load of mail handling for a particular user. So the $HOST idea is not
bad, though the logfile names are getting kind of long.
Another idea: Some of us use the temporary backup trick that generates
file names like ..../Mail/backup/msg.xtOF It wouldn't be hard to generate
..../Mail/logs/msg.xtOF from $LASTFOLDER. Then you'd have a nearly
useless log file containing only the beginning part of the log for all
messages, plus one logfile with short name per message containing the
rest.