Courier cannot start:

Courier service can not be started: courierlogger dead but pid file exists
#service courier-pop3s status

In the Plesk Control Panel/Tools and Settings/ Services all of the ‘Courier’ entries show they are not running.

The usual fix of grep the courierlogger process and killing it does not work. Here is what does:

This is caused by hung processes, but not courierlogger was hung, but couriertcpd processes, one of them was running since April 3:

# ps aux | grep couriertcpd
root 3784 0.0 0.0 11976 1796 ? S 11:05 0:04 /usr/lib64/couriertcpd -address=0 -maxprocs=40 -maxperip=4 -nodnslookup -noidentlookup 110 /usr/sbin/pop3login /usr/lib64/plesk-9.0/pop3login Maildir
root 3907 0.0 0.0 11972 1884 ? S 11:05 0:00 /usr/lib64/couriertcpd -address=0 -maxprocs=40 -maxperip=4 -nodnslookup -noidentlookup 143 /usr/sbin/imaplogin /usr/bin/imapd Maildir
root 3973 0.0 0.0 11972 1776 ? S 11:05 0:00 /usr/lib64/couriertcpd -address=0 -maxprocs=40 -maxperip=4 -nodnslookup -noidentlookup 993 /usr/bin/couriertls -server -tcpd /usr/sbin/imaplogin /usr/bin/imapd Maildir
root 26808 0.0 0.0 103396 2080 pts/2 S+ 19:53 0:00 grep couriertcpd
root 26951 0.0 0.0 11976 1704 ? S Apr03 0:49 /usr/lib64/couriertcpd -address=0 -maxprocs=80 -maxperip=10 -nodnslookup -noidentlookup 995 /usr/bin/couriertls -server -tcpd /usr/sbin/pop3login /usr/lib64/plesk-9.0/pop3login Maildir
[root@216-55-187-88 ~]# ps aux | grep courierlogger
root 13394 0.0 0.0 4124 1432 ? S 18:08 0:00 /usr/sbin/courierlogger -name=courier-authdaemon -pid=/var/run/courier-authdaemon.pid -lockfile=/var/lock/subsys/courier-authdaemon -start /usr/lib64/courier-authlib/authdaemond

Kill all those processes and after that you are able to start the service successfully:

# service courier-imapd status
courierlogger (pid 29099) is running...