IMAP Extension '+' folder email addressing with Postfix and Procmail

Howdy -- yeah I unfortunately don't know exactly how that procmailrc file would look in order to accomplish what you're after -- but we can certainly help make sure that procmail is being used, and that the .procmailrc file is being read. Once we have that working, all you'd have to do is develop the procmailrc syntax.

The first thing we'd want to do is verify that Postfix is configured to use procmail for mail delivery.

To do that, you can run this command:

postconf -n | grep mailbox_command

It should be using procmail-wrapper.

As far as the .procmailrc file goes -- yes, for an email user, that would go into $HOME/homes/USERNAME/.procmailrc.

You do not need a .forward file.

You would want to make sure the .procmailrc file is owned by the user and group of your email user.

Also, if there are any errors in the .procmailrc, those would show up in /var/log/procmail.log. You may want to review that log to see if any errors are displayed when sending an email to that particular user.

At some point in the past I had set this up for my personal email user on a Virtualmin installation, by putting the proper commands in its individual .procmailrc, located in /home/domain/homes/user. If I recall correctly, I didn't have to make modifications in the global or domain procmailrc.

Indeed you need to modify the delivery command of Postfix, like the forum post you linked explains. For me, it reads

mailbox_command = /usr/bin/procmail-wrapper -o -a $DOMAIN -a "$EXTENSION" -d $LOGNAME

The relevant contents of my procmailrc are as follows:

EXT=$2
:0
* EXT ?? ^^sent^^|^^sent\-mail^^
$HOME/Maildir/.$EXT/

This should cause Procmail to put the mail into the IMAP subfolder when the recipient is "user+folder@domain.tld". The part after the "??" is a Procmail-syntax regular expression that limits the allowed folders to certain names, here "sent" and "sent-mail". Note that there should be a backslash before the "-" in "sent-mail"! The forum software swallows that for some reason.

The regexp is there to prevent "random" IMAP folders from getting created when some joker sends mail to "myuser+crapfolder@domain.tld". :) (Without that restriction, Procmail would simply create the folder, if it doesn't exist yet!)

The procmail log would suggest that it is trying to use /var/www as the user's home directory... which is probably wrong. :) Can you please verify the home directory for the mail user in question, to be found in the /etc/passwd file.

Okay, I have to admit I'm stumped then why Procmail would assume /var/www as home directory. It sure has to get that directory name from somewhere. Maybe for some reason it's being executed as a different user whose homedir IS /var/www...

It might help if you posted your full /etc/postfix/main.cf, your /etc/procmailrc and the user's individual procmailrc, as well as log excerpts from /var/log/mail.log and /var/log/procmail.log and /var/log/syslog at the time of delivery attempt.

Hmm, while in theory you shouldn't need this -- you could always try adding these two lines to the top of your user's .procmailrc file:

That would explicitly set the email location

Okay, I went over your config files and the logs.

First, the thing you noticed, the "to/orig_to" line in the mail log, is okay this way. Virtualmin configures Postfix to use virtual domains as opposed to "real", "mydestination" ones. It maps users like "user@domain.tld" to "locallinuxuser@hostname.domain.tld", which in turn Postfix detects as local user and delivers it to their mailbox.

One difference between your config and mine is the two lines ":0 $DEFAULT" at the end of your global procmailrc. Those are not there in my procmailrc files, so you might want to try removing them. As far as I know Procmail syntax, those two lines define a delivery rule that unconditionally puts the mail into the default folder. I'm not sure if Procmail rules are processed on a first-match or best-match or last-match basis, but if it's first-match, that rule would override all subsequent ones that try to put the mail in a subfolder.

In your procmail.log, I noticed that the error messages occur AFTER the "folder" line, which to me kinda seems like at that point Procmail already made the choice where to put the email, and that the errors are like a follow-up issue and not directly related to the IMAP folder selection.

So you might try removing the two lines from your global procmailrc as stated above, maybe that helps.

Aah, this looks good! You probably just need to tell Thunderbird to subscribe to / show the newly created IMAP folder. They don't usually do that by themselves when a folder just "appears out of thin air". :) So you need to enter their folder management, probably do a "refresh", and then subscribe to the folders.

If that doesn't help, the next debugging step would be to take a look at the file system on the server, if the mails have been stored in their proper directories there. You should see one file per email.

Yay, glad it works now! And yeah, my example was for IMAP folders on the root level, as opposed to subfolders of INBOX or similar. :)