Emails with attachments are delayed – KB10391041


Description:  Emails are being delayed by hours or even days.

Common customer description: We are receiving emails a lot later than we should.  Sometimes days later.

Probing questions:

When did this start?
Did you recently get a spam filtering service like Securence?
Is everyone affected?
Do the emails that are delayed have attachments?

Steps to isolate: If the client recently signed up and started using a spam filtering solution make sure emails without attachments arrive on time.  If regular emails arrive quickly but emails with attachments are delayed proceed to the next step.

Steps to resolve: Check Exchange and the clients firewall for spam filtering and virus scanning attachments.  Since Securence and other name brand spam filtering solutions scan the emails for infections along with spam, these tasks do not need to be performed in Exchange or on the firewall.

Additional considerations: It has been found that once the spam filter solution is finished scanning the email it opens a socket with the Exchange server.  Exchange is expecting the email to be transmitted within a certain amount of time.  If something like a firewall is also set to scan attachments prior to allowing the transmission Exchange will close the socket due to timeout.  Eventually the email will get sent through if enough attempts move fast enough to beat the timeout.  Better to just leave the filtering to the spam filtering service.

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