Multiple Ip addresses for rDNS

We currently have a customer who has 2 adsl lines through a watchguard which is splitting and directing the traffic for outages.

They have their mail setup to only send from 1 line (say IP 1.2.3.4 - line 1) which has a reverse dns setup for mail.domain.com

If line 1 goes down, and we let the mail go out of line 2, the rdns will be incorrect, as its going out of  ip 5.6.7.8 which has a reverse dns of mail2.domain.com - even though the servers banner is mail.domain.com

Is there any way to have the rdns to 2 different IP's? or is there a better setup?

Thanks
stevie_deeAsked:
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FastFngrzCommented:
I'd recommend asking the ISP if they'll relay SMTP for you, that way it doesn't matter!
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footechCommented:
Why not just have the ISP change the PTR record for the 5.6.7.8 IP so that it points to mail.domain.com.  There shouldn't be a problem with multiple PTR records pointing to the same FQDN.
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Jessie Gill, CISSPTechnical ArchitectCommented:


You could do the below or you will have get the ISP to relay for you or use a third party


Mx = 10 = mail.domain.com

A = mail.domain.com = 1.2.3.4
A = mail.domain.com = 5.6.7.8

With the above email will be using round robin to look up mail.domain.com but it will always go to your watch guard at which point the watch guard will send the mail to exchange.

Now the Rdns for both ip addresses should be mail.domain.com. So if you do end up switching they will still both have Rdns records.  Thus if line one fails, email will not be lost since now the email server trying to send will not be able to find the server it should do another lookup and get the other a record 5.6.7.8 and then connect to your watch guard.   This is how I believe DNA will behave
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