In case if you are experiencing a mail flow problem very frequently on your exchange environment because of your Exchange hub transport service is getting stopped; you probably may wanted to check the free disk space as it may be a problem due to the log pile up under this location C:\inetpub\logs\LogFiles\W3SVC1.
Even if you get to analyze the event logs you may find below events as well.
Event ID: 12025
Event Source: MSEXchangeTransport
Transport service is disconnecting performance counters with process lifetime from their old process.
Event ID: 7001
Event Source :MSEXchangeTransport
The service will be stopped. Reason:Insufficient disk space in ‘C:\program Files\Microsoft\Exchange Server\V14\TransportRoles\data\temp’.
What are these log files?
These are the IIS log files generated by the exchange service. Generally, deleting this log files will not affect your exchange environment however it is recommended that you may keep at-least a month’s log files.
So if you wish to avoid an unnecessary downtime it’s better to schedule a job to delete these old files from this folder. Use below command line if you wish to automate this task.
forfiles.exe /P C:\inetpub\logs\logfiles\W3SVC1 /S /M u_ex*.log /D -30 /C “cmd /c del @file”
If you wish to increase the log retention period simply increase the number D -180 on above command. Visit in case of emergency.