On 17/06/2015 10:33 p.m., Ted Cooper wrote:
On 17/06/15 18:16, Kurt Jaeger wrote:
I had a case where lb1-smtp-cloud3.xs4all.net delivered to an A record
where an MX existed.
Exchange machines will also try this if all MX defer, but if they get a
4xx/5xx error they ignore it. It's quite annoying but otherwise benign.
If there was as client which paid attention to the random A host
responses (when not 2xx), it would an issue.
I once had Hotmail ignore the MX record that everyone else used, and try
the non-host A. This wasn't the right MX, so hotmail senders got
'relaying denied' errors whilst everyone elses email delivered OK.
I was forced to remove the non-host A to mitigate the issue, which is
annoying when folks expect websites to work without 'www'.
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