Error sending email from a application to exchange online server

[noi_1979]

HI, I´m getting this error when I´m trying to send email from a application which is hosted on internal server to exchange online server, using mail.protection.outlook.com:

Failed to send e-mail notification: Error in processing. The server response was: 4.4.3 Temporary server error. Please try again later ATTR3.1 [VE1EUR01FT044.eop-EUR01.prod.protection.outlook.com]
System.Net.Mail.SmtpException: Error in processing. The server response was: 4.4.3 Temporary server error. Please try again later ATTR3.1 [VE1EUR01FT044.eop-EUR01.prod.protection.outlook.com]

[#2]

@noi_1979  Have you checked other applications (on your on-premise) if they are able to relay the mails to O365. if not it is a Connector issue on your On-premise or some configuration change. But looking at the Error code , it looks like some temporary error. Can you remove the IP from the Connector , Run IISRESET from Exchange Server, Wait for 10 minutes. re-add the ip on your connector and Test again to see if it works ?

Cheers

Ankit Shukla

[#3]

@noi_1979 

AFAIk either your sending IP's are blocked at MS or may be your mails are getting throttled.... would recommend to open a case with MS.

Thanks

Robin Nishad