The remote host is vulnerable to a buffer overflow.
The remote host is running Exim, a message transfer agent (SMTP). It is reported that Exim is prone to an IPv6 address and a SPA authentication buffer overflow . An attacker exploiting those flaws may be able to execute arbitrary code on the remote host. Exim must be configured with SPA Authentication or with IPv6 support to exploit those flaws.
Upgrade to version 4.44 or higher.