Exchange 2016 Back Pressure

What are the resources available on the Exchange server ... how many CPU/cores, memory, disk space available?

How is your paging file configured ... amount of RAM + 10MB?

Take a look at these references if you haven't already...

• https://technet.microsoft.com/en-us/library/bb201658(v=exchg.150).aspx
• http://exchangeserverpro.com/exchange-transport-server-back-pressure/
• http://msexchangeguru.com/2013/07/29/troubleshooting-backpressure/

I have 4 cores, cpu is at 10%
16GB memory, setting at 79%

Disk space for my exchange drive 602GB 96GB free.

pagefile 16GB

The error is pointing to disk space and I'm trying to determine how it is calculated since I have 96GB free.

The formula is

100 * (<hard drive size in MB> - 500 MB) / <hard drive size in MB>

In your case

100 * ( 602 x 1024 - 500) / (602 x 1024) = 99% which is roughly 7gb of free space you should be fine with 96 gb no matter what, are you sure it is not on another drive?

More info https://technet.microsoft.com/en-us/library/bb201658(v=exchg.160).aspx

Thats what I thought, my C: is 100GB with 28GB free.  It only has the OS installed.  

The error points to D:  

I have CU1 installed, I know CU3 has been released.  I wonder if its a bug.

Really curious behavior.... Any chance you had something filling out the disk and now it's not anymore or are you still seeing this behavior?

I had to disable it through the EdgeTrasport.exe.config and restart the transporter service in order for mail to work.  its still disabled.

Re reading your OP you said it is only rejecting external emails so it is in the medium range and not high

But even though for 602 gb 96% that's 24 gb free space

Resource            : PrivateBytes
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=75 HighToMedium=73 LowToMedium=72 MediumToLow=71]
Pressure            : 4

Resource            : QueueLength[SubmissionQueue]
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=15000 HighToMedium=10000 LowToMedium=9999 MediumToLow=2000]
Pressure            : 0

Resource            : SystemMemory
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=94 HighToMedium=89 LowToMedium=88 MediumToLow=84]
Pressure            : 79

Resource            : UsedVersionBuckets[D:\Microsoft\Exchange Server\V15\TransportRoles\data\Queue\mail.que]
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=1500 HighToMedium=1000 LowToMedium=999 MediumToLow=800]
Pressure            : 2

Resource            : DatabaseUsedSpace[D:\Microsoft\Exchange Server\V15\TransportRoles\data\Queue]
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=99 HighToMedium=97 LowToMedium=96 MediumToLow=94]
Pressure            : 86

Resource            : UsedDiskSpace[D:\Microsoft\Exchange Server\V15\TransportRoles\data\Queue]
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=99 HighToMedium=90 LowToMedium=89 MediumToLow=80]
Pressure            : 86

Resource            : UsedDiskSpace[D:\Microsoft\Exchange Server\V15\TransportRoles\data]
CurrentResourceUse  : Low
PreviousResourceUse : Low
PressureTransitions : [PressureTransitions: MediumToHigh=99 HighToMedium=90 LowToMedium=89 MediumToLow=80]
Pressure            : 86

So now you are at low and no backpressure however you are at 86 % and backpressure will move to medium at 89% (following your output) that's 3 % breathing space which might be the trigger / issue

And, as you can see,  when it moves to medium you need to go back under 80% to revert to low. I guess you had a temporary peak in the disk utilization above 86%

This makes sense, thank you.