The remote IMAP server is affected by a buffer overflow vulnerability.
The remote host is running Ipswitch IMail Server, a commercial messaging and collaboration software product for Windows. According to its banner, the version of Ipswitch installed on the remote host has a buffer overflow issue in its SMTP server component. The details of the exploit are not currently known. An attacker exploiting this flaw would send a malformed SMTP command to the server. Successful exploitation would result in arbitrary code being executed.
Upgrade or patch according to vendor recommendations.