This indicates an attack attempt against a Buffer Overflow vulnerability in the Quiksoft EasyMail SMTP Object.
The vulnerability is caused by an error in the "EasyMailSMTPObj" ActiveX control, in "emsmtp.dll", when the vulnerable software handles a specially crafted argument to the "SubmitToExpress" method. It allows a remote attacker to execute arbitrary code.
Quiksoft EasyMail Objects 'emsmtp.dll' 6.0.1
PostCast PostCast Server Pro 3.0.61
System Compromise: Remote attackers can execute arbitrary code on vulnerable systems.