moving email server, ATT is asking for two A Records

Hi Experts,

We've got an A Record for our mail server and an associated MX record. We are moving to a new location and will have a new IP address. ATT hosts our DNS and they won't let me create an MX record that is associated with an IP address. it has to be associated with an A Record.

My question is: can we have two A Records for one email server - mail.our_domain.com?
I can ping the new IP address at the new modem at the new location, but there is no server set up there.

Will we lose email with two A Records when there is only one server connected to one of those IPs?

thanks! Kristin
forcedexposureAsked:
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Scott GorcesterCTOCommented:
You can have multiple A records with different URL's poining to the same IP, but you would not want to create multiple A records with the same URL pointing to different IP addresses.

Not exactly sure what the specifics over your question is? Can you provide more detail?

Scott Gorcester MCITP
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Will SzymkowskiSenior Solution ArchitectCommented:
You can have as many MX records you want for a specific domain. However they are all based on priority so you would have mail1.domain.com = priority 1 and mail2.domain.com = priority 2. When the first MX is not available it will use the second one.

So you cannot have two MX recrods routing mail to different mail servers. Also DNS MX records do not route mail or load balance.

If the MX recrod is not reachable on the domain the sender will receive an NDR so they will be notified and they will need to re-send the email.

Will.
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forcedexposureAuthor Commented:
ATT just set us up with multiple A records for the same domain: mail.mydomain.com, but with two different IP addresses.
The IP address in the new location, which we have not moved into yet, has a running modem with one of those IP addresses.
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Will SzymkowskiSenior Solution ArchitectCommented:
Ok so if at your current location you have MX pointing to xx.xxx.xxx.12 and MX at your New site with xx.xxx.xx.13 as long as the priority for .12 has a higher priority than .13 mail will continue to go to .12 until it is not reachable. At this time you will need to have your Mail server up and running at your new location.

What you could do is setup the new mail sevrer in the New location and then when you are ready just change the priority of .13 higher than .12 and mail will flow to the new mail server.

This does take time to propegate on the internet.

Will.
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Scott GorcesterCTOCommented:
Will is correct that you can multiple MX records with different priority levels but this is not the same as your A records.

Scott Gorcester MCITP
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Scott GorcesterCTOCommented:
Can ATT support explain what their intention is here?

Scott
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Scott GorcesterCTOCommented:
Also curious to know if they provided instructions on how to configure the A records, for instance you could have an A record for "email.domain.com and autodiscover.domain.com.

Scott
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Don ThomsonCommented:
Each of your MX records should have a Priority Number.  The current location should have a lower priority number than the new location for now.  

You said that you don't have a server at the new location yet.  
When you shut down the current server to  move it you have no where to send mail. It will try the lower priority umber IP then the higher priority number IP
once the server is on line at the new location  then you can remove the MX number
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forcedexposureAuthor Commented:
Here's our current DNS configuration:
Name       Type       Data       
      SOA       cbru.br.ns.els-gms.att.net.       
      NS       cbru.br.ns.els-gms.att.net.
      NS       cmtu.mt.ns.els-gms.att.net.

@.       A       website server IP address that sends emails       
mail.       A       router IP address at old location       
mail.       A       router IP address at new location      
www.       CNAME       mydomain.com.       
@.       MX       10 mail.mydomain.com.       
@.       MX       20 mail.mydomain.com.
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Will SzymkowskiSenior Solution ArchitectCommented:
So as i stated originally, all you need to do is change the priority of the MX recrod that is pointing to your new SIte with a HIGHER priority and mail will start to flow after the external DNS updates.

Will.
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Scott GorcesterCTOCommented:
I suspect they are leveraging Round Robin DNS, have a look here.

https://support.microsoft.com/en-us/kb/168321

Scott
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forcedexposureAuthor Commented:
Yes, AT&T was using Round Robin, which could've meant that I would lose email. I deleted that. AT&T's policy is to not do any DNS provisioning for IP addresses that they do not own. This means I need to go to Comcast to get them to add the info.

So now i wonder if i can get Comcast to add a second A Record for mail2.mydomain.com with matching PTR record AND  an associated MX record for mail2.mydomain.com?

If i do that, do i need to make changes to our inhouse Exchange server? i'd think not, but it's not clear.

thanks! Kristin
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Dave HoweSoftware and Hardware EngineerCommented:
AT&T are in fact correct - you aren't supposed to supply IP addresses for MX records (although it's a common thing to do, and almost all mail servers support it because, well, it's a common thing to do)

I would suggest setting up newmail.domain.com as an A record for the new server, and giving it a higher priority number than the old one.

once the old IP is switched off, set the mail.domain.com A record to point to the same IP as newmail; give that a few days to settle out, then delete the MX record pointing at newmail.domain.com., and the A record.

If you round-robin them, the seeking mail server is going to get it wrong 50% of the time, which isn't good.
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Scott GorcesterCTOCommented:
Personally I would prepare the new location, move the mail server over after hours and change my MX and A records. We have done it this way hundreds of times and have never had any complaints.

Scott
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forcedexposureAuthor Commented:
Yes, but it appears that AT&T hosts our DNS records and they can't set matching PTR record because they don't own the new block of IP addresses at the new location.
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Dave HoweSoftware and Hardware EngineerCommented:
that's not a problem either. you don't need a one-stop-shop for dns - go to whomever owns your new range, and ask them either to delegate your range or set the reverse (ptr) records to a name of your choice.  Latter is to be preferred of course - Delegation would require you to have a server to delegate to (and I have found AT&T have two responses to anything you ask - charge you for it, or say they can't do it. sometimes both)
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