This indicates an attempt to exploit a buffer-overflow vulnerability in GLD Postfix.
The vulnerability is caused by an error when the vulnerable software handles a long string passed to the "client_address" property. It allows a remote attacker to execute arbitrary code via sending a crafted packet.
GLD Postfix older than version 1.5.
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the latest update from the vendor.