The remote host is vulnerable to a flaw that allows for the bypassing of authentication.
The remote host is running the ArGoSoft Mail Server. This version of ArGoSoft is prone to a remote, unauthenticated access flaw. Specifically, as ArGoSoft does not require authentication prior to serving the 'addnew' script, an unauthenticated user can perform administrative tasks. Successful exploitation would lead to the attacker being able to add accounts and escalate their privileges on the remote server.
Upgrade or patch according to vendor recommendations.