The remote host is vulnerable to a Denial of Service (DoS) attack.
According to its banner, the remote sendmail server is running a version less than 8.13.7. There is a flaw in versions of Sendmail less than 8.13.7 that would allow a remote attacker to deny resources to legitimate users. An attacker exploiting this flaw would only need to be able to send email through the remote sendmail server.
Upgrade to version 8.13.7 or higher.