I often get to configure IMAP on mail environments. The easiest way to test if it works is to use telnet (using built-in or Putty).
First, connect to port 143:
telnet IMAPserver.domain.com 143
Then run the following to authenticate, list mails and quit. Just change whatever you need in red, domain is not always needed if you have one domain.
* OK The Microsoft Exchange IMAP4 service is ready. . LOGIN DOMAIN\username password . OK LOGIN completed. . SELECT Inbox * 2 EXISTS * 2 RECENT * FLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent) * OK [PERMANENTFLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent)] Permanent flags * OK [UNSEEN 2] Is the first unseen message * OK [UIDVALIDITY 10638] UIDVALIDITY value * OK [UIDNEXT 220] The next unique identifier value . OK [READ-WRITE] SELECT completed.
. . LOGOUT