There are several reasons why due to back pressure that your incoming email might stop. I ran into one of them today on my very own SBS 2008 server. How embarrassing…so I thought I would blog about it.

In the morning when I got up and checked my email I was shocked to see only 3 new emails instead of the usually 30+. I wiped the blur from my eyes and noticed that all three email were from my own internal network. I first checked the usual suspects. Is my Internet up? Did my IP address change? Is my MX record still there? Is my firewall working correctly? Yes, yes, yes and yes. Time to look at the event logs and the Exchange server. Exchange server says my stores are mounted and Outlook says so too.

The event log had a story to tell. Fortunately for me the event log on this server is very clean otherwise I could have easily overlooked the error message that led me to the solution because it only occurs one time.  It’s Event ID 15006 Source MSExchangeTransport.

The Microsoft Exchange Transport service is rejecting message submissions because the available disk space has dropped below the configured threshold.

Resource utilization of the following resources exceed the normal level:
Queue database logging disk space ("C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue\") = 97% [Medium] [Normal=95% Medium=97% High=99%]
Physical memory load = 92% [limit is 94% before message dehydration occurs.]

Back pressure caused the following components to be disabled:
Inbound mail submission from the Internet
Mail submission from the Pickup directory
Mail submission from the Replay directory

The following resources are in the normal state:
Queue database and disk space ("C:\Program Files\Microsoft\Exchange Server\TransportRoles\data\Queue\mail.que") = 96% [Normal] [Normal=95% Medium=97% High=99%]
Version buckets = 0 [Normal] [Normal=80 Medium=120 High=200]
Private bytes = 3% [Normal] [Normal=71% Medium=73% High=75%]

As you can see the message is pretty detailed and tell you exactly what the problem is, except be sure to read the whole thing. At the top is says that transport service has stopped and is rejecting message submissions because the available disk space has dropped below the configure threshold. While it’s true the disk space was an issue it wasn’t enough to create the stop. Physical memory load was the problem. And the solution was, as Eriq pointed out in a earlier blog post and screencast, to reduce the amount of memory that Sharepoint and Monitoring databases are allowed to use on the server.

Read Eriq’s blog post here: http://www.thirdtier.net/2009/08/setting-the-maximum-memory-usage-on-the-sharepoint-database/

And what his screencast demonstrating the procedure here: http://www.thirdtier.net/screencasts/limit-sharepoint-database-memory-usage/

Note that after applying the fix, I had to restart the Exchange Transport service to get my incoming to start flowing again.

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