Hi,

My setup is Exchange 2013 CU5 on Server 2012 fully patched running on vmware 5.1 fully patched. The server supports around 50 users, has 16GB of memory, a 16GB page file and fast disk access to dedicated disks on a SAN. My vmware host has 96GB of memory and around half is in use.

A few times today we got MSExchangeTransport warnings about resource pressure relating to 'version buckets' around the same time someone sends a large attachment (around 40MB). We have generous sending limits at 50MB due to the nature of our work.

The full message is...

...

The resource pressure increased from Normal to High.

The following resources are under pressure:
Version buckets = 330 [High] [Normal=80 Medium=120 High=200]
Physical memory load = 93% [limit is 94% to start dehydrating messages.]

The following components are disabled due to back pressure:
Inbound mail submission from Hub Transport servers
Inbound mail submission from the Internet
Mail submission from Pickup directory
Mail submission from Replay directory
Mail submission from Mailbox server
Mail delivery to remote domains
Content aggregation
Mail resubmission from the Message Resubmission component.
Mail resubmission from the Shadow Redundancy Component

The following resources are in normal state:
Queue database and disk space ("C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\data\Queue\mail.que") = 58% [Normal] [Normal=95% Medium=97% High=99%]
Queue database logging disk space ("C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\data\Queue\") = 58% [Normal] [Normal=95% Medium=97% High=99%]
Private bytes = 4% [Normal] [Normal=71% Medium=73% High=75%]
Submission Queue = 0 [Normal] [Normal=2000 Medium=4000 High=10000]
Temporary Storage disk space ("C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\data\Temp") = 58% [Normal] [Normal=95% Medium=97% High=99%]

Task Manager shows memory usage at 90% (14.4GB of 16GB)

We recently migrated from Exchange 2010 (with 8GB memory) and had no issues with back pressure.

I ran get-messagetrackinglog to cover a few minutes either side of this event being logged. There were around 150 entries. A single email was over 40MB in size. There were also multiple lines showing the same email, which does not reflect in the users mailboxes (for example a single autoreply was sent from one user, but the get-messagetrackinglog showed 11 results). I have posted a question about this here also...

https://social.technet.microsoft.com/Forums/en-US/6425aa7a-4957-487e-ad7c-6aec5fe50379/getmessagetrackinglog-multiple-results-for-single-email?forum=exchangesvradmin

If a single large email caused the back pressure to kick in how can I prevent this happening in future? I don't want to simply limit my attachment size (as mentioned this was fine on Exchange 2010 and 2003 before that)

I checked EdgeTransport.exe.config and noted the following default entries

<add key="DatabaseMaxCacheSize" value="512MB" />
<add key="DatabaseCheckPointDepthMax" value="384MB" />
<add key="QueueDatabaseLoggingBufferSize" value="5MB" />

Would increasing these help?

Lastly, I have read this article (http://eightwone.com/2011/04/06/limiting-exchange-2010-sp1-database-cache/) and wondered whether it would be beneficial to implement a limit on the database cache? If so, what should I be aiming at for my setup? And is this relevant for Exchange 2013? (I don't see a performance counter for Database Cache Size Min, or Max under 'MSxchange Database')

Advice greatly appreciated.

I've seen the same thing... not sure of the fix.. my email was limited to 35MB but someone tried sending over 2GB internally. Can't find where to track it though

Found this in a different Exchange forum; worth reading.  This thread was marked as answered.  Good luck.

https://social.technet.microsoft.com/Forums/en-US/c3d300c5-473f-4ab3-8df2-e85c0ea2ed99/backpressure-activated-after-exchange-cu5-installversion-buckets?forum=exchangesvrsecuremessaging