Thanks for the excellent diagnostic technique. Here is the result:

telnet xxx.xxx.xxx.xxx 143
Trying xxx.xxx.xxx.xxx...
Connected to xxx.xxx.xxx.xxx.
Escape character is '^]'.
* OK CommuniGate Pro IMAP Server 5.1.12 at melx.becknet.com ready
abc CAPABILITY
* CAPABILITY IMAP4 IMAP4REV1 ACL NAMESPACE UIDPLUS IDLE LITERAL+ QUOTA ID MULTIAPPEND LISTEXT CHILDREN BINARY LOGIN-REFERRALS UNSELECT STARTTLS AUTH=LOGIN AUTH=PLAIN AUTH=CRAM-MD5 AUTH=DIGEST-MD5 AUTH=GSSAPI AUTH=MSN AUTH=NTLM
abc OK completed

The STARTTLS is in  there. Let me see if I can disable it somehow.