Hi all, On the 5th of October we noticed a spike in delivery failures at domains hotmail.com, outlook.com, msn.com, and live.com. The failures were caused by DNS lookup errors reported by the MTA as "5.4.4 (unable to route: no mail hosts for domain)”. This is problematic as the error is reported as hard bounce causing many addresses to be suppressed.
Delivery to other Microsoft domains was fine. The issue also occurred between 20-24 September and now again on the 5th of October. Since then, delivery has been normal. We noticed that Microsoft is using DNS entries for MX hosts with a very short TTL (30 sec) and rotating IP addresses. We think the short TTL may be related to the issue. Aggressive caching of the MX-es seemed to help. Did anyone else experience this issue, or knows about recent DNS changes at Microsoft? Thanks, Maarten _______________________________________________ mailop mailing list mailop@mailop.org https://chilli.nosignal.org/cgi-bin/mailman/listinfo/mailop
