Missing Mail Accounts

From Mac OS X Server FAQ

Server Admin's mail accounts section only shows users that have sent or received mail. After you have setup the mail accounts send a few test emails and the accounts will magically show up in the accounts section.

A corrupted quota file may also prevent the full list of accounts from showing up under the Maintenance tab, since Server Admin builds this list by running /usr/bin/cyrus/bin/cyrus-quota. If the list stops at a certain account, look at the quota file for the account that should have been presented next, under /var/imap/quota/ by default. If it's something other than a pair of integers, replace the file. It may help to fix quota inconsistencies after doing this, with

/usr/bin/cyrus/bin/cyrus-quota -f