The remote host is vulnerable to multiple attack vectors.
The remote host is running a vulnerable version of Clearswift MAILsweeper for SMTP. Clearswift MAILseeper for SMTP versions 4.3.19 and prior are reported prone to several security issues. According to the vendor, an attacker can bypass security or render the application unavailable for legitimate users.
Upgrade to version 4.3.20 or higher.