Exchange 2010 - Back Pressure - Inbound mail stopped. Event ID 15004

markpalinux used Ask the Experts™
Exchange 2010 Server ( Rollup 4) with CAS/HUB/Mailbox ( member of DAG. ) inbound mail flow stopped.

The Event log warning follows... this is related to Back Pressure.

Question if memory is an issue for back pressure at 94% and Exchange store by default will take 90% , how much room does that leave for other services ?

The links below discuss settings in the EdgeTransport.exe.config , note this is not an Edge Transport, however the EdgeTransport.exe is running and I assume that is normal.
Server has 24 GB of Ram. Running Exchange 2010 , Symantec Endpoint.
Page file is set to allow Windows to manage, init size 24, max 36.

Understanding Back Pressure
This version is the Exchange 2010,printer%29.aspx

Understanding Back Pressure
Exchange 2010 Service Pack 1

Event Log
Warning      9/14/2010 1:37:57 PM      MSExchangeTransport      15004      ResourceManager

The following resources are under pressure:
Version buckets = 120 [Medium] [Normal=80 Medium=120 High=200]
Physical memory load = 96% [limit is 94% to start dehydrating messages.]

The following components are disabled due to back pressure:
Inbound mail submission from the Internet
Mail submission from Pickup directory
Mail submission from Replay directory
Mail delivery to remote domains
Content aggregation

The following resources are in normal state:
Queue database and disk space ("C:\Program Files\Microsoft\Exchange Server\V14\TransportRoles\data\Queue\mail.que") = 30% [Normal] [Normal=95% Medium=97% High=99%]
Queue database logging disk space ("C:\Program Files\Microsoft\Exchange Server\V14\TransportRoles\data\Queue\") = 31% [Normal] [Normal=94% Medium=96% High=98%]
Private bytes = 1% [Normal] [Normal=71% Medium=73% High=75%]
Batch Point = 0 [Normal] [Normal=1000 Medium=2000 High=4000]

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It is not the issue with Memory, it is the issue with disk space, Please go through the article, it will help you in understanding the issue of BackPressure and also the solution for it.

Please go through it and revert back if you have any issues.
Tony JohncockLead Technical Architect

In my own experiences this has tended to be because backups aren't being taken properly rather than disk space actually being an issue.

Logs don't get purged and the disk fills so it might be worthwhile checking your backups are running ok.

Of course - you might need to provision more disk. :)

Thanks for the feedback. I looked at Disk space first - this is/was not a disk space issue. All drives have a few gb of free disk space.

If you look again at the Event log message above - it seems to show each category that Exchange had issues with ...

The following resources are under pressure:
Version buckets = 120 [Medium] [Normal=80 Medium=120 High=200]
Physical memory load = 96% [limit is 94% to start dehydrating messages.]

It also stated which were under a normal condition.

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To add
During the problem Telnet to port 25 showed “450 4.3.1 Insufficient System Resources”
Tony JohncockLead Technical Architect

It could still be disk related:

Number of Uncommitted Message Queue Database Transactions in Memory
A list of changes that are made to the message queue database is kept in memory until those changes can be committed to a transaction log. Then the list is committed to the message queue database itself. These outstanding message queue database transactions that are kept in memory are known as version buckets. The number of version buckets may increase to unacceptably high levels because of an unexpectedly high volume of incoming messages, spam attacks, problems with the message queue database integrity, or hard disk performance.

When Exchange starts receiving messages, these messages are grouped together in batches and then prepared as version buckets. If an incoming message has a large attachment, it can be separated into multiple batches. These batches that are being processed are known as batch points. The number of outstanding batch points can exceed the set thresholds, especially when there's an unexpectedly high volume of incoming messages with large attachments.

When version buckets or batch points are under pressure, the Exchange 2010 transport server will start throttling incoming connections by delaying acknowledgement to incoming messages. Exchange will reduce the rate of inbound message flow by tarpitting, which introduces a delay to the MAIL FROM commands. If the resource pressure condition continues, Exchange will gradually increase the tarpitting delay. After the resource utilization returns to normal, Exchange will gradually start reducing the acknowledgement delay and ease into normal operation. By default, Exchange will start delaying message acknowledgements 10 seconds when under resource pressure. If the resources continue to be under pressure, the delay is increased in 5-second increments up to 55 seconds.

Exchange 2010 keeps a history of version bucket and batch point resource utilization. If the resource utilization doesn't go down to normal level for a specific number of polling intervals, known as the history depth, Exchange will stop the tarpitting delay and start rejecting incoming messages until the resource utilization goes back to normal. By default, the history depths for version buckets and batch points are in 10 and 300 polling intervals respectively.

Taken from: which might be worth going through as it discusses everything it could be.

Also - sure you don't have a large message stuck in there?

I looked at the tracking logs and didn't see any large messages around that time.
Tony JohncockLead Technical Architect

Is your transport service running?
I will post more, I have disabled back pressure ( I do  understand this is not recommended )  no problems with the server to date.
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This question has been classified as abandoned and is being closed as part of the Cleanup Program. See my comment at the end of the question for more details.

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