This article applies to:

• Trustwave MailMarshal (SEG)

Question:

• A single outbound message is sent to a large number of recipients/domains
• Delivery of other inbound and outbound messages is slow

Information:

The MailMarshal sender service is used for both inbound and outbound delivery. If a user sends outbound "bulk" mail (a single message sent to many users and domains), delivery of inbound messages could be affected because the sender is busy with a large number of domain deliveries.

Suggested Resolutions:

MailMarshal does not currently offer message throttling by direction or by sender address.

The following ideas can assist with this situation. All solutions assume that the source of the delay is limited sender connections, and that sufficient bandwidth is available.

1. Consider bypassing MailMarshal for outbound bulk mail. If the mail is being sent by dedicated newsletter software and not from a user's mail client, routing through MailMarshal offers little gain and bypassing MailMarshal has little risk.
2. Adjust the Sender Threads (Advanced System Properties > Server Threads, also available to set on each processing server if required). Increasing Static Route threads may help to prioritize inbound messages in most cases.
3. Use the Message Parking function in MailMarshal to delay delivery until out of hours. Message parking is specifically designed to address this issue.
   • Use a rule to identify the offending bulk messages by sender and/or total bandwidth required. See Trustwave Knowledgebase article Q10893.
4. Install an additional MailMarshal node dedicated to this traffic (if the mail is being sent from a dedicated source).
   • You can use a virtual machine or install the software on a physical server that does not have heavy network usage.
5. Deliver through the Microsoft SMTP service bound to a separate IP address and/or port on the MailMarshal server.
   • Use a rule to identify the offending bulk messages by sender and/or total bandwidth required. Use the "set routing to host" action to deliver the messages to the Microsoft SMTP Service instance. Place this rule last in the outgoing policy evaluation.
   • This rule shifts responsibility for outbound message delivery for these messages.