We use SMTP2GO to relay scan-to-email messages from employees' home office copiers into our Microsoft 365 tenant. It worked reliably for more than a year, but since Monday—around the time of the Microsoft 365 outages—messages have been showing as "processed" in SMTP2GO for more than 12 hours without arriving in Microsoft 365. I'm the only administrator, and there haven't been any configuration changes. I already opened a support ticket and tried allowlisting SMTP2GO's IP addresses. Having SMTP2GO rotate the sending IP helped for one scan, but the delays returned. Regular inbound mail to the tenant appears normal. Has anyone dealt with this, or have suggestions for troubleshooting whether the problem is on the SMTP2GO or Microsoft 365 side?
3 Answers
Since SMTP2GO marks the messages as processed, it has accepted them for delivery, but that status doesn’t necessarily mean Microsoft 365 has received them. Check message trace in Exchange Online for one of the delayed messages and compare the timestamp and recipient. If there’s no trace at all, Microsoft 365 may not be seeing the connection; if there is a trace showing filtering or deferral, it should reveal the next step.
Double-check the Microsoft 365 connection filter allowlist rather than assuming the IPs were all added successfully. Make sure every SMTP2GO range is included and that the recommended safe-list option is enabled under Defender’s Connection Filter Policy. The web interface only accepts one range at a time; pasting the entire list may appear to save but can result in none of the addresses being retained. Adding the ranges individually or through PowerShell is more reliable. In a similar case, messages started delivering immediately after the complete list was added.
First, confirm whether the problem is specific to your Microsoft 365 tenant. Try sending a scan to an external address hosted somewhere other than Microsoft 365. Also check SMTP2GO’s delivery logs for the actual handoff status. If external delivery works but Microsoft 365 messages remain delayed, that points more toward Exchange Online filtering or a service-side issue than the scanners themselves.
I haven’t tested an external non-Microsoft 365 recipient yet, but that should help narrow it down. The copiers are at users’ homes, so testing them remotely is a little difficult. Normal inbound mail is working, and this started right after the Microsoft 365 outages.