Mail Does Not Send
A common problem is finding that mail is not sending correctly and that the /var/spool/clientqueue is filling up with files. This directory can actually shut down your server if you do not have a separate directory for /var when this happen. The speed at which this happens is determined by the amount of mail that is being sent.
Cause of the Problem:
The cause of the problem is most often a mis configured firewall or a mis configured tcp_wrappers.
The firewall should allow connections on port 25 for Postfix, port 143 for IMAP (web based email) and port 110 for POP3. Check your firewall that these are open.
Here is an example of a tcp_wrappers hosts.allow from a working Mail Server. Note that the is mail server does not allow POP3 but allows IMAP, and POSTFIX .
#
# hosts.allow   This file describes the names of the hosts which are
#               allowed to use the local INET services, as decided
#               by the ‘/usr/sbin/tcpd’ server.
#
POSTFIX:       ALL
SMTP:   ALL
IMAP:   ALL

Cannot Create Mailboxes
Even if cyrus IMAP is set up correctly there are times when the user cyrus cannot login to create a mailbox. If the password is correct the problem is probably related to /etc/hosts.allow/
Add this line to etc/hosts.allow
ALL: 127.0.0.1

Savemail Panic
If you see the error “Losing.lqfj54koqLM019255:savmail panic”
or
“savemail: cannot save rejected email anywhere”
Add this line to etc/hosts.allow
ALL: 127.0.0.1