I'm troubleshooting an issue where a user is not receiving messages from multiple AOL and Yahoo senders. I have access to the organization's Microsoft 365 tenant, and test messages sent from AOL bounce back with only this generic notice: "Unable to deliver message after multiple retries, giving up." There is no SMTP status code or other diagnostic detail.
The messages do not appear in Exchange Online Message Trace, while the recipient receives mail from other senders normally. The recipient domain's MX records also appear to be correct. Does this indicate that AOL or Yahoo is failing before completing the SMTP handoff to Microsoft 365? Could the recipient address or domain be blocked in their outbound systems, and what troubleshooting steps are available when the bounce contains no useful diagnostic code?
3 Answers
If the messages are completely absent from Message Trace, Exchange Online almost certainly never accepted them. That points to a failure on AOL or Yahoo’s side—possibly DNS resolution, an SMTP connection problem, TLS negotiation, routing trouble, or their retry process giving up. The generic bounce was generated by their mail system, not Microsoft 365.
There is not much the recipient-side administrator can do with this particular NDR. Confirm the recipient domain’s MX records independently and make sure the Message Trace search covers the correct time zone and date, but if normal mail is arriving and these messages never appear, the tenant is unlikely to be rejecting them. The sender needs to troubleshoot with AOL or Yahoo support.
A recipient address being specifically blacklisted by AOL is possible, but the bounce does not provide enough evidence to confirm that. “After multiple retries” generally means their servers repeatedly failed to connect to or route toward the destination and eventually generated their own nondelivery report. Without a real DSN or SMTP status code, the sender’s provider will need to investigate the delivery logs.
That was my conclusion too, but AOL and Yahoo are not including any SMTP code or additional diagnostic information in the bounce.