Exchange 2016 Back Pressure

I had issues with my exchange server today where it would sporadically stop receiving emails from our enterprises management system, photocopiers and UTM appliance, I found out what the issue was and thought it would be good to share this with other users

Exchange 2016 has a feature called Back Pressure which seems like a very good idea but caused me a major headache.

I was getting errors

453 4.3.1 insufficient resources on the UTM

and exchange transport errors explaining the were disconnecting external connections

This command showed me the issue

Powershell

[xml]$bp=Get-ExchangeDiagnosticInfo -Process EdgeTransport -Component ResourceThrottling; $bp.Diagnostics.Components.ResourceThrottling.ResourceTracker.ResourceMeter

which produced

Text

Resource            : PrivateBytes
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=75 HighToMedium=73 LowToMedium=72 MediumToLow=71]
Pressure            : 15

Resource            : QueueLength[SubmissionQueue]
CurrentResourceUse  : High
PreviousResourceUse : High
PressureTransitions : [PressureTransitions: MediumToHigh=15000 HighToMedium=10000 LowToMedium=9999 MediumToLow=2000]
Pressure            : 20606

Resource            : SystemMemory
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=94 HighToMedium=89 LowToMedium=88 MediumToLow=84]
Pressure            : 82

Resource            : UsedVersionBuckets[C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\data\Queue\mail.que]
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=1500 HighToMedium=1000 LowToMedium=999 MediumToLow=800]
Pressure            : 0

Resource            : DatabaseUsedSpace[C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\data\Queue]
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=99 HighToMedium=97 LowToMedium=96 MediumToLow=94]
Pressure            : 61

Resource            : UsedDiskSpace[C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\data\Queue]
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=99 HighToMedium=90 LowToMedium=89 MediumToLow=80]
Pressure            : 61

Resource            : UsedDiskSpace[C:\Program Files\Microsoft\Exchange Server\V15\TransportRoles\data]
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=99 HighToMedium=90 LowToMedium=89 MediumToLow=80]
Pressure            : 61

as you can see from the QueueLength[SubmissionQueue] it is over the medium to high bracket and because of this it stops receiving emails until the threshold is reduced. I did have 79GB free on the local drive but this made no difference so what I ended up doing to fix this was:

Create another drive (mine was 100GB but unsure on specific requirements) on the SAN and attached it to the exchange server then migrated the Queue to it.

for full details read the attached site

http://missingsmth.com/exchange-2016-back-pressure-troubleshooting/

Thanks to:

https://community.spiceworks.com/topic/1969054-exchange-2016-back-pressure