Changing hosts without changing Microsoft e-mail servers
March 24, 2011 9:26 AM   Subscribe

Question about transferring hosting service without disrupting Microsoft e-mail.

A client wants me to move their hosting from a slow server to Dreamhost. The domain registration will stay the same. What do I need to know about DNS records to make sure I don't interrupt the company's Microsoft Outlook mail?
posted by Victorvacendak to Technology (4 answers total)
You're wording this funny. I assume you mean you are changing mail servers and want this to be transparent to your users.

DNS takes time to propogate. Sure, you can mess with settings to try and make it go faster, but really, I wouldn't count on it. I've seen people handle this many different ways. Whenever I move someone's mail server I do the following:
  1. Check to make sure everything is 100% at the old server. (Seriously, skip this and you'll wonder why something isn't working when it wasn't working in the first place.)
  2. On Friday, I set up the new server with everything ready to go. All the accounts are created, all the settings set as appropriate, it's 100%, just no one knows about it yet.
  3. On Saturday at 2am, I redirect all incoming SMTP connections (incoming emails) from the old server to the new. Usually, iptables is fine for this. Windows? Don't use it, but I've heard Windows can do everything Linux/BSD can and more, so I'm sure you'll figure it out or someone will chime in with the best way. Now the new server is getting all the new mail. No new mail should hit the old server.
  4. 2:05am, I start copying over all the emails that were already on the old server to the new server. Depending on the server software used (Dovecot, Courier, etc), I'll change exactly what I use to copy the mail and leverage some bash script to automate large migrations. See also imapsync.
  5. 4am, check the status, most migrations are done well before now unless you're moving multiple TBs of data. You are using gigabit networking to move large amounts of data, right?
  6. 4:05am, check all the mailboxes, make sure everything looks OK.
  7. 4:15am, redirect all incoming POP and IMAP connections (clients checking mail, who uses POP these days?) from the old server to the new server. Make sure the mail clients (Outlook, et al) are in fact going to the new server and everything appears as normal.
  8. 4:20am, change the DNS.
  9. Monday 9am, DNS should have propogated, verify that traffic to the old server is non-existant, then decomission.
  10. The migration part should take about an hour of actual work.

posted by Brian Puccio at 10:26 AM on March 24, 2011

Response by poster: Sorry for the unclear post. But thanks for the night-owl timeline--I'm always trying to figure out how this stuff is done without disrupting service.

What's happening is that I'm not moving the mail server. Or at least I don't think I am and want to make sure the change in webhost doesn't do anything to e-mail. After I wrote this question, I realized the domain possessed MX records that point to some third-party mail server.

So those mail records I will not touch. I just plan on moving the website name servers to,, and so on. I guess I am just looking for possible unforeseen complications, where I accidentally break mail or some other service.
posted by Victorvacendak at 5:52 PM on March 24, 2011

Response by poster: To clarify that, I don't intend on moving the mail server. I guess if the MX record stays the same, everything is fine, right?
posted by Victorvacendak at 5:55 PM on March 24, 2011

Ah-ha. I understand you better now.

You have There's an A record and an MX record for You want to change the A record for and since you want to move your web server to a faster server. You do not want to disrupt any other services in the progress. Yes, if you just change the IP address for the A records for and, then the fact that you have an MX record setting the mail server hostname to and an A record for won't be affected (effected?).

Just reconfigure your domain name server config (if you're not running your own name server, you might have your registrar handling that end for you) to change the A records for and and over a short period of time, people will start hitting the new web server. You can adjust the TTL in advance to try and speed it up, but it doesn't sound like it's a big deal.
posted by Brian Puccio at 6:57 PM on March 24, 2011

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