[CentOS] Sendmail-SMTP, Cyrus-IMAPD and plus (+) addressing.

Has anyone on this list got sendmail and cyrus-imapd configured so that email addressed in the form username+folder@example.com gets delivered directly to cyrus' user.username.inbox.folder?

I have been tinkering with this on and off for about a week and no matter what I have tried, all traffic addressed in the +folder format ends up in user.username.inbox instead.

If anyone has gotten this to work then I would very much appreciate knowing the exact steps that you followed to implement it.

1. I am not changing smtp MTAs, the legions of fans of qmail and postfix notwithstanding.

2. Ditto for imap and dovecot.