courier-imapd or dovecot services cannot be started: Address already in use

Symptoms

Cannot start courier-imapd service:

# service courier-imapd start
courier-imapd: bind: Address already in use

OR

Cannot start Dovecot service:

# service dovecot start
Starting Dovecot Imap: Error: service(pop3-login): listen(*, 110) failed: Address already in use
Error: service(pop3-login): listen(*, 995) failed: Address already in use
Error: service(imap-login): listen(*, 143) failed: Address already in use
Error: service(imap-login): listen(*, 993) failed: Address already in use
Fatal: Failed to start listeners
[FAILED]

Cause

Something else is using the port already

# netstat -tulpn | grep 143
udp 0 0 0.0.0.0:143 0.0.0.0:* 1564/portreserve

Resolution

1. Connect to the server via SSH.

2. Stop portreserve:

   # service portreserve stop
   Stopping portreserve: [ OK ]

3. Start courier-imapd/dovecot service:

   # service courier-imapd restart

4. Turn off portreserve start at boot:

   # chkconfig portreserve off - For CentOS 6 and older
   # systemctl disable portreserve - For CentOS 7