Messages from some or all sources are delayed or fail to be delivered. When searching the Message Audit Logs for the sending IP via the Control Center Status > Message Audit Logs you find:
Potential causes:
The "abort message" action is logged when there is an interruption of the SMTP mail delivery either from a connection timeout or due to an SMTP protocol violation by the sending server.
If you need to engage Broadcom support to assist in investigating the issue, please collect the following information in order to facilitate the investigation:
For "protocol deviation" related delivery issues, also see this article: "421 esmtp: protocol deviation" and "Abort" action for inbound messages listed in Message Audit Logs