Exchange - Mail.que utilizing more space - Exchange Drive - Out of Space

The Mail.que database file in Exchange Servers increases drastically after a point of time is an expected behavior, below are the possible reasons for them.

Data stored in Mail.que file:

• Email message live traffic
• Shadow queue
• Emails pending for delivery & Submission queue

Use the below path to reach the mail.que database file,

Note: It is highly advisable to exclude this path from AntiVirus scanning.

%ExchangeInstallPath%\TransportRoles\data\Queue

Mail.que utilizing high space:

• Emails in queue due to sudden flooding during peak business hours or unavailability of other Exchange server
• Increased message expiration time, nethold time. The cmdlets to re-configure these values are in below article

Note: The mail.que database file will not shrink, however during the online maintenance WhiteSpace will be accumulated which could be used for future emails 

How to re-create Mail.que database file?

Re-creating the mail.que database file will not harm your Exchange server or data loss if we follow the below routine.

1. Check the queue in the Exchange server,

Get-Queue

2. Pause 'Microsoft Exchange Transport' service to drain the emails in the queue and ensure emails in queue are completely Null.

Note: Do not stop the service until the emails are drained

3. Once after all the emails are drained, we may Stop the 'Microsoft Exchange Transport' service.

4. Go to the below path in your server, rename the mail.que file to mailold.que.

You may move out this mailold.que file to another dive and retain it in case if you need it for any backup purposes.

%ExchangeInstallPath%\TransportRoles\data\Queue

5. Then Start 'Microsoft Exchange Transport' service, once then the mail.que file will be re-created in the specific folder. Make sure, you run the Get-Queue cmdlet and mailflow is working as expected. 

6. If you do not want to re-create the mail.que file size, you may extend the drive size to accommodate them.

TransportConfig Settings:

Run the below cmdlet to update the global transport configuration, to keep the mail.que size limited. 

Get-TransportConfig | FL SafetyNetHoldTime

Update the SafetyNetHoldTime to safe limit based on the requirement of your organization. 

Set-TransportConfig -SafetyNetHoldTime 1.00:00:00

SafetyNetHoldTime - Specifies how long a successfully processed emails are hold.