SUBMISSION QUEUE - HIGH Due to Back Pressure on Exchange 2016 Server

Very recently - have come across the issues like mail submission queue count was so high due to back Pressure  

Back pressure is component for inbuilt monitor system which is available from exchange 2010 version 

In Exchange, be it Exchange 2010, Exchange 2013 or Exchange 2016, you might have come across back pressure alerts or where Exchange just won't function. This includes:

• Disk space

• Memory

• 15004

• 15006

Microsoft Exchange Transport is rejecting message submissions because the available disk space has dropped below the configured threshold. The following resources are under pressure:
Used disk space ("C:\Microsoft\Exchange Server\V15\TransportRoles\data\Queue")
Used disk space ("C:\Microsoft\Exchange Server\V15\TransportRoles\data")
Overall Resources
The following components are disabled due to back pressure:
Mail resubmission from the Message Resubmission component.
Mail submission from Pickup directory
Mail submission from Replay directory
Mail resubmission from the Shadow Redundancy Component
Inbound mail submission from the Internet

In Event Viewer  application log - you may receive the below event ID's which indicates your exchange transport service affected with back pressure 

 

Below is a sample error logged for a space issue on the Server:

Event 15006, MSExchangeTransport

Resolution: After housekeeping done in Exchange drives where queue database resides. in my case its E: drive. i removed some logs and files and queue become normal.