In my case Application was using Port 25 and using the app custom connector on load balanced Exchange 2016 servers and message rate limit was set to unlimited.
Get-ReceiveConnector SERVERNAME\* | FT Name,bindings,MessageRateLimit |
Solution –
Late realized its the Client proxy connector causing the bottleneck. Increased from 5 which is the default value . Changed to 30.
NOTE : Below Commands sets the rate limit for all Exchange servers in the environment. Use Servername\ for specific server.
Get-ReceiveConnector "*\Client Proxy*" | FT Name,*RateLimit* |
Get-ReceiveConnector "*\Client Proxy*" | Set-ReceiveConnector -MessageRateLimit 30 |
if you have issue on Port 587 IMAP mail submission- you should increase Rate Limit on below connector
