I've been facing some challenges recently with the SMTP Relay feature in Exchange Online. Various internal services that rely on this for sending notifications have been intermittently failing to deliver emails. Interestingly enough, testing the settings never reveals any issues; they work perfectly during those checks. I've come across log entries that indicate a 'server connection error (Code 107)', but I haven't been able to pinpoint the exact cause. Furthermore, there haven't been any announcements regarding outages from Microsoft or similar reports from other users. I've checked the DNS, NTP settings, and firewall rules, and everything appears to be set up correctly. Has anyone else been running into similar SMTP Relay problems?
3 Answers
I've got a few thoughts – though they're more speculative than definitive. Have you considered whether Microsoft 365 or Azure is enforcing TLS 1.2? This might explain the connection issues you’re facing. Also, make sure you're not using an old endpoint meant for legacy TLS; that could definitely mess things up. Plus, since you're using SMTP Relay, it sounds like the EWS shouldn't be an issue. Check if your on-premise Exchange Server might have throttling that’s causing blocks. It could be Microsoft having some flaky moments too!
Thanks for the ideas! I think it's likely due to NTP settings, as incorrect time settings can cause delivery errors. I need to check all the services to ensure none of them are misconfigured.
I had a similar issue pop up just yesterday. My 365 connector suddenly stopped working with a system like Veeam. The connector allows emails from certain IPs without authentication, so I know that's not the problem here.
That’s interesting! I’m using a similar setup for internal purposes without OAuth2, and while it generally works, I've noticed some inconsistencies lately.
Could it be related to a spam filter? Sometimes these filters can block emails unexpectedly. Double-check that everything is unblocked and there’s no quarantine interfering. It might be prudent to validate your SPF and DKIM settings as well—though if you already ruled that out, it might not be the cause this time.
I appreciate the thought! Everything appears fine on our end—no blocked or quarantined messages. However, it's strange that the method works most of the time.
Regarding the on-premises Exchange throttling, I've been upgrading several systems due to similar issues—those clients rely on SMTP relay through hybrid servers to connect to 365.