If a user mistypes an email address when they send it to your domain, or just guesses at a valid domain email address, their email is likely to be bounced. You may wish to set up a “catch all” email address so these emails are accepted. Note, if you set up a catch-all email address, it is likely that you will receive unsolicited (spam) email.
Most of the information available for setting up postfix with a catch-all account uses the virtual-user set of features of postfix. Dovecot uses actual unix users, so it does not make sense to activate the virtual user system and re-enter all the dovecot users.
Here’s how you set up postfix to have a catch-all email account that operates with dovecot. The account will receive all of the mail that is sent to an email address which doesn’t exist. In other words, it will potentially receive a lot of spam, but it is sometimes important for business reasons to be thorough and receive the occasional mistyped email address.
Assuming dovecot and postfix is installed, first make the user which will catch the mail:
# useradd catchall # passwd catchall
Then add or change these lines in /etc/postfix/main.cf:
local_recipient_maps = luser_relay = catchall
Now restart postfix:
# /etc/init.d/postfix restart
…and you should be sorted. To check the catch-all inbox, use imap/pop or webmail, using the ‘catchall/yourpassword’ account details.
Source: http://ubuntuforums.org/showthread.php?t=1156313
