Having issues connecting on prem smtp server to exchange online

Copper Contributor

I have an on-prem SMTP server which is being used by an application to email invoices.  The on prem server was setup with a connector and was working successfully.   Recently I had to change ISP which changed the public address.   I believe I changed everything properly and DNS lookups are successful.  However, I am not routing email.  I read a few articles which indicate I may need a new CA Certificate from Exchange online however I'm not able to find where I would generate that certificate.  Any feedback would be helpful.

3 Replies



Please take a look at Connector to see whether an update needed such as IP address


Thanks.  Yes I updated the connector with the new IP address.  I didn't do the original setup, so I'm not sure if there was a CA or not.  My documentation indicates I need a CA from the exchange online server, however, MS documentation indicates I need a CA from my onprem server


I needed to download M365 certs to my on prem server and delist the new IP from Microsoft.  Then is worked