If I change a nameserver but preserve the MX record will it harm email?

Question

My client already has email setup with a provider but would like their website hosted by a different provider. Currently they just have a NS record pointed at the company that hosts their email. I used dig to grab their two MX records, otherwise they don't have any other records set. They are using Network Solutions as their domain registrar so I'll have to use Network Solutions advanced DNS tool to make the changes.

I was planning on doing the following: 1. Change the NS to point at Network Solutions (this is a requirement of their Advanced DNS) 2. Make sure the MX records point at the old email host 3. Add A records for the new website host

When I click the edit advanced DNS button in the Network Solutions control panel it says the following:

"Please Note: When you Move Name Servers to Network Solutions, your Existing Name Servers will no longer be used. As a result, Web sites and E-mail from other providers will be lost."

That last word has me kind of concerned. Will all the previous emails actually be "lost" or are they saying that email sent during the change over might be lost?

Solution 1

Contrary to what Wooble says, the wording is quite sensible. The case that it addresses, of course, is fairly obvious with a little thought: Someone adjusts the name server records to switch from another company's content DNS hosting service to Network Solutions' content DNS hosting service without copying any of the existing other records across, and all of a sudden HTTP and SMTP go awry, as the world at large is no longer told the right places to contact for these services.

Yes, people sometimes do not know that it's necessary to transfer the database across from one publisher to another when one switches publishers.

And contrary to what spacehunt says, things will not soft fail if you switch the servers before copying the database. In the absence of MX resource records, SMTP Relay clients will fall back to A and AAAA resource records, per RFC 2821 § 5. They won't be there, of course, since you haven't copied them over either. The SMTP Relay clients will bounce all queued mail as undeliverable. Soft failures occur in the event that DNS query resolution fails to get an answer at all, not in the event that query resolution succeeds and gives a zero records answer.

In a similar vein, do you know that it isn't necessary to switch DNS hosting companies if all that you want to do (This is what you've told us.) is point HTTP service somewhere else? As you've explained it, what you're doing seems entirely unnecessary. You have company A providing SMTP mail service and content DNS service for the client, and company B providing content HTTP service. To make company B's services known to the world, it's not necessary at all to replace company A with a company C — Network Solutions. Just go to the current content DNS service provider and enter the necessary A and AAAA resource records into the database.

Solution 2

As long as the MX records are not changed, no, your emails will not be lost.

At worst, the SMTP server that tries to send email to you won't be able to resolve your domain name's MX records for a while, but all that happens is that the emails get queued on their side to be retried again later.

Solution 3

Your DNS provider (unless you're using bundled services) has no control whatsoever over your actual web and email services; the wording there is incredibly stupid. You will not lose any data stored on other servers by changing your DNS.

If the new DNS host has the same A, CNAME, and MX records as the old provider, it's extremely unlikely you'd even have any connectivity problems; your hostnames will resolve to the same IPs before and after your change propagates. If you're using different DNS records on the 2 DNS hosts, it's possible some of your traffic may go to unexpected IPs for a time about equal to your TTL setting; you should be prepared to deal with traffic continuing to go to the old IPs for a short while.