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Mail Delivery Delayed - 4.4.7, eventually fails to send.

3rik7 (IS/IT--Management) (OP)
2 Feb 12 11:03
We've recently noticed an uptick in mail that is getting delayed and eventually fails to send to certain domains with a timeout error. In the past, I always told the user it was a problem with the receiving mail server but I'm now not convinced that is the case. A user sends an email from their work account to an external recipient. They get the delay message. A day later, they get the failed message. They try the same thing with their personal email account, the mail immediately goes through successfully. No settings, internal or external, have changed.

With limited knowledge, I think my research has revealed that it may be an external reverse DNS problem? Using the mxtoolbox.com smtp test, everything comes back green with the exception of one yellow warning which is " Warning - Reverse DNS does not match SMTP Banner". Using the reverse lookup tool on that site returns this for the domain name - "ip67-155-84-99.z84-155-67.customer.algx.net" which is obviously not our domain name.

That algx.net thing resolves to XO Communications, who is our ISP (I think...because we actually get all of our internet and MPLS circuits through a company called Mitel Solutions but I think they are just resellers of XO internet circuits?)

So my question is...does that reverse DNS look right or should it resolve to something like mail.ourdomain.com?
Also, if it should be changed, I'm not exactly sure who to call or what to tell them to do. We use NetSolutions to host our external DNS, MX records and all that.

As a side note, mxtoolbox.com is reporting that we show up on 1 blacklist out of 103. Could that be part of the problem?

Any help/advice would be appreciated.

Thanks,
Erik

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