Adding a Subject with Procmail

Lately I've been corresponding a great deal with someone who doesn't elect to use the Subject: line in emails. When responding to this emails my mail application, mutt, uses the Subject line: re: your mail. Mutt also groups conversations into threads using (among other things) the Subject line. So every reply to every person who has sent a message with a blank subject line gets grouped into a single thread when they, in fact, have nothing to do with one another.

I decided to create Subject lines for incoming messages without them on the fly using the standard procmail tool. This pair of recipes does the trick:

:0 fhw
* ^Subject:[\ ]*$
|formail -i "Subject: Your email ($$)"

:0 fhw
* !^Subject:
|formail -i "Subject: Your email ($$)"

The $$ gets turned into a low number (the process id actually) which is unique enough to keep threads separate. The resulting Subject lines look like: Subject: Your email (1024) } and have been working quite well.

There's probably a way to use a single recipe to catch both cases (blank Subject and no Subject), but I hate procmail's almost egrep and just settled on this.

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