ptr record

We have 2 lines from our ISP in our network.

We had Line 1 go down and traffic failed over to Line 2 no problem, except for email. Users were receiving NDR's and we were suddenly being blacklisted by Barracuda.
Called our ISP to verify if we had correct ptr records pointing to both WAN links.
We had one ptr record pointing to the(Line 1) barracuda.domain.com and Line 2 was pointing to our mail domain name.
When we failed over and were blacklisted I think it's because when mail servers did a reverse dns lookup on us it pointed to our mail.domain ptr record.
But why wouldnt that be accepted?
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tolinromeAsked:
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Mahmoud SabrySenior IT Systems EngineerCommented:
A PTR record is what lets someone do a "reverse" DNS lookup - that is, they have your IP address and want to know what your host/domain is, so that they receive emails only from its correct mail server
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muffCommented:
Usually it is sufficient that the PTR record is present, not even that the reverse resolution produces the same domain as the email (consider a shared hosting environment where there can be hundreds of domains being served out of a single mail server, and so a single IP.  The reverse lookup will be one of these domains).

So I suspect it was something else causing the rejects.  Do you have any more detail?
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shauncroucherCommented:
Ensure that the EHLO greeting matches your rDNS and make sure your rDNS on line 2 is forward confirmed.

See my article here:

http://exchangeshell.wordpress.com/2010/03/12/exchange-send-connector-ehlo-and-dns-data-rdns-ptr-mx-spf-txt-a-record

Shaun
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