18.11 Setting Mail Quotas and Deleting Stale Mail

Because qmail's mailboxes are normally in each user's home directory, any quota scheme that applies to the user's files automatically includes the file(s) in the mailbox. For many purposes, this is all the mail quota that's needed. You may want to apply Jeff Hayward's quota exceeded patch to qmail-local that recognizes an over quota error and treats it as a hard error so mail is bounced back to the sender, rather than a soft error so mail stays in the queue.

For POP toasters, the vpopmail package discussed in Chapter 13 includes code to enforce mail quotas. If you build your own simpler POP-only system, use the mailquotacheck script in .qmail files to check quotas as mail is delivered. (All these have links at www.qmail.org.)

You may also want to set a policy for stale mail, so that mail is deleted from the server after some period of time. If you use Maildirs, this is very easy to implement, because each message is in a separate file with a timestamp. In each Maildir, messages in the new subdirectory haven't been read, and messages in cur have been read and left on the server. My policy is to delete unread mail after a month, on the theory that if you don't look at your mail once a month, you'll probably never look at it at all, and to delete read mail after three months. This is easily arranged with a couple of shell commands to run every day or every week. While you're at it, you might as well delete mail that's been marked deleted (the T flag in the filename) or moved into the Trash subfolder. If all the user directories are under /home:

cd /home {    # unread mail over a month old      find /home/*/Maildir/new -type f -mtime +30 -p    # read mail over three months    find /home/*/Maildir/cur -type f -mtime +90 -p        # any mail marked deleted    find */Maildir -type f -name "*:2,*T*" -print    # any mail in Trash/new or cur    find */Maildir/.Trash/??? -type f -print } | xargs -t rm

If your Maildirs are somewhere else, modify the find commands appropriately to look where they are. By adding a few more commands, you can add policies like deleting mail from a spam subfolder after a week and other subfolders after some other amount of time. With slightly fancier programming, probably in Perl, it's also straightforward to delete the oldest files from a Maildir until the user is under quota. The elegance of the Maildir design makes this all much easier than with mboxes because nothing has to be locked or rewritten, and the cleanup can proceed safely while mail deliveries are going on.