The remote host is running ClamAV.
Clam AntiVirus (ClamAV) is a free and open-source, cross-platform antivirus software toolkit able to detect various types of malicious software, including viruses. One of its main uses is on mail servers as a server-side email virus scanner. Traffic observed from this remote host indicates it is running clamAV.
Ensure that the installation runs the latest version of ClamAV and that it is updated with the latest security definitions available.