On 2016-02-21 01:40, Adrian Neale (iComms) wrote:
Hi there, just joined to try and get some knowledge/help on an issue when getting emails delivered from (particularly) Hotmail/Outlook.com but occasionally Gmail addresses. I consulted RFC5321 and it does say the mail delivery will be tried in order of MX preference. *What we are finding is that 90% of Hotmail/Outlook.com emails sent to the domain abc.com are coming from mxbackup.3rdparty.com. All other domains behave as expected and come in via 0 autodiscover.abc.com. Some Gmails follow this behaviour too.*
I haven't observed any issues with these providers, however, Facebook's "Add an email" verifications consistently use the lowest priority (highest numbered) MX, which has caused us a fair amount of issues as our lowest MX will tempfail most requests when the primary MX is reachable. If I change the MX records to only list the primary MX, the email is delivered instantly.
Other Facebook mail is received successfully, it's just this one class (and possibly password resets or other account verifications, I'm not sure)
I don't see any issues from the providers you named though, and given our configuration, we would absolutely notice fairly quickly if one of the major providers suddenly couldn't email us.
Do you see any connection attempts or delivery attempts that could indicate Hotmail/Outlook is trying your server first?
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