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Mail Migration DNS Question

We currently have a large number of clients who we manage mail hosting for. We are about to move to a new mail provider and I have a question about the changes we need to make to DNS to have this happen as efficiently as possible.

Our current clients all have an entry in their zone file as follows (actual domain names have been changed):

ourcustomer.com MX IN 300 mail.ourmailserver.com. [Preference = 10]

mail.ourmailserver.com is a domain name we control and currently it as has an A record for mail.ourmailserver.com which points to the IP address of our current mail server.

My question is - if we migrate our mail to a new provider do we need to update the MX record for all our customers individually or can they stay as they are and have us just make a change on our domain for where mail.ourmailserver.com points to? If so, what would the change be?

The other complication is that many of our customers also have an A record created as follows:
mail.ourmailserver.com. A IN 300 XX.XX.XX.XXX
Where XX.XX.XX.XXX is the IP address of our mail server.

I presume we would have to delete these records?

I am not a DNS expert and would really appreciate some views on this.

Thanks

David
0
red500
Asked:
red500
2 Solutions
 
jar3817Commented:
None of your customers should have to make any changes. You'll only need to change the "A" record for mail.ourmailserver.com to point to the new IP address. You might want to lower the TTL (time to live) on that record first to something like 300 seconds so the changes will be seen quicker.

The fact that some of your customers have these records: "mail.ourmailserver.com. A IN 300 XX.XX.XX.XXX " is problem and they shouldn't. They'll either need to delete or update those records to see the new server.
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Bruno PACIIT ConsultantCommented:
Hi,

A big part of the mail servers on Internet make some tests on incoming e-mail to check for spam. One of these tests can be a Reverse DNS check to verify that the name of the server that emits an e-mail is matching with its IP address.

If you change your server IP addresses, you have to change the A record pointed by the MX record to continue receiving e-mail, BUT YOU ALSO need to modify RR record for your mail server so that the e-mail you send won't be refused by a Reverse DNS test.

In your example, you will change the A record for mail.ourmailserver.com to a new IP aaa.bbb.ccc.ddd, so you also need to change the PTR DNS record (the reverse DNS record) for aaa.bbb.ccc.ddd to point to "mail.ourmailserver.com".


Have a good day.
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