The host is running Sendmail and is prone to Buffer Overflow Vulnerability.
Successful exploitation will let the remote attacker to create the mangled message by execute arbitrary code, and can cause application crash.
Upgrade to version 8.13.2 or later http://www.sendmail.org/releases
Buffer overflow error is due to improper handling of long X- header.
Sendmail Version prior 8.13.2
Updated on 2017-03-28