Outbound messages with more than 52 recipients are not being accepted my Messaging Gateway (SMG) and Message Audit Logs (MAL) shows the message as "message aborted".
This is a known issue with the mail server in the SMG 10.7 releases. When the sending mail server uses PIPELINING to speed up SMTP delivery, if there are more than 52 recipients in the SMTP communication, SMG closes the network connection.
This issue has only been identified in environments running Exchange 2007.
A workaround for this issue can be installed by Broadcom support which disables the PIPELINING option. Please contact Broadcom support for assistance.