This indicates an attack attempt to exploit a Buffer Overflow vulnerability in MDaemon Email Server that was disclosed by Shadow Broker as Easyfun exploit.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application. A remote attacker may be able to exploit this to execute arbitrary Operating System Commands within the context of the application.
MDaemon/WorldClient pre 9.5.6
System Compromise: Remote attackers can gain control of vulnerable systems
Currently we are unaware of any vendor supplied patch for this issue.