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?