[ Thanks to Andrew
Weber for this link. ]
“Of course you need to set up the hosts for the mail servers
that you want to monitor. The first service is a check on IMAP port
143 with a timeout of five seconds and it searches for a text
string ‘OK’ which is part of the response of the IMAP server to a
connection request. The second service is for IMAPS and it shows
the port listing there as port 993 while it searches for a more
detailed text string in ‘Dovecot ready’. That search string
specifically indicates that Dovecot, the MDA (Mail Delivery Agent),
is ready to communicate. Searches are case sensitive and you will
need to place specific text in these searches that relate to your
MDA and the ports you are using.”