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In early January of 2023, we started experiencing issues where one of our applications cannot send out some of their emails using the Office 365 SMTP relay. We receive errors such as "Access Denied" and "Suspicious Activity has been detected and sending has been temporarily restricted for further evaluation". The messages are never released, they never show up, and message traces do not show the attempted emails at all. The application does not have the ability to specify a username or password at all. It also cannot use TLS. Did MS change the behavior of the Office 365 SMTP relay and are we able to adjust settings? I cannot find any SMPT relay settings in our Azure tenant at all. Thanks, Bryan
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Hello,
SMTP Relay settings are available in Exchange Online server.
Admin Microsoft 365 > Exchange Online > Mail flow > Connectors
I suggest you to check there your SMTP Relay configuration
At the moment Microsoft 365 doesn't permit you to enable SMTP Relay (you can just create them).
You maybe need to confirm existing settings.
Did you specify a source IP for your SMTP Relay? Regards
I did find a relay connector and the option is chosen to verity the IP address matches one of the following. They do seem to match a single IP on this list, which is the address they are NATed or PATed out with and which every user uses, so I am not sure why the error is occurring. I wanted to verify that this actually is the relay they are using, as specified in their software settings, but I cannot find the DNS name or IP address of the relay anywhere in the Exchange Admin.