So if you've followed Joel's excellent article on installing cyradm to manage Cyrus, you might find you want to be able to send email directly to shared mailboxes.
Some mail clients bork out on the default setting, so I've done this:
add this line to /etc/imad.conf
postuser: postuser
Use cyradm to create a shared mailbox, and assign “anyone” the “p” privilege, like this:
localhost> create MySharedMailbox localhost> setacl MySharedMailbox anyone p
Restart the IMAP server, and you can then address mail to:
postuser+MySharedMailbox@my.server.address
and it will automatically be delivered straight to that folder.
I use this for Quarantine-Virus, Quarantine-Spam folders that let the IT staff see what mail is being rejected for what reason, as we don't send alerts for spoofing viruses.