The remote host is vulnerable to a buffer overflow.
The remote host is running Alt-N MDaemon, a SMTP/IMAP server for the Windows operating system family. It is reported that versions up to and including 8.0.3 are prone to multiple buffer overflow vulnerabilities. An attacker may cause a denial of service or execute arbitrary code on the remote server. The attacker does not need credentials to exploit the flaw in CRAM-MD5/LOGIN authenticate method.
Upgrade to version 8.0.4 or higher.