After changing our public IP we are having problem relaying to one of our domains. Our on-prem exchangeserver (used only for relay) get the following error in the message queue.
"Last Error: 451 4.7.500 Server busy. Please try again later from [x.x.x.x]. (AS77713200) [HE1EUR04FT016.eop-eur04.prod.protection.outlook.com]".
It's a scanner that have worked fine prior to the change of public IP change but now all mails from this scanner now gets stuck at our on-prem Exchange server. Outlook klients have no problem and scanners that send mail to our other domains.
- We have updated our SPF records for all domains.
- Tried to create a IP whitelisting in O365 when sending from the relayserver.
Regards,
Magnus