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Email DNS Question

Hi -

We're in the process of migrating email from our local servers to Google Apps - and I'd like it to be as seamless as possible for our clients.  

Currently - in their email progs (outlook, thunderbird) - they are pointing to:

server: mail.ourdomain.com
smtp server: mail.ourdomain.com

So - it's the same.

On google - they specify:

server: imap.googlemail.com
outgoing: smtp.googlemail.com

I was *hoping* to be able to make it as seamless as possible by just changing the DNS records on our server to have an A record for mail.ourdomain.com point to google...but can I?  Since our current server is using that same record for both incoming and outgoing - and google has two different addresses (imap and smtp) - can I do that?

Is there any way given this scenario for me to do a DNS pointer that will accomplish this change on the client end seamlessly w/o having them change their account settings?

Thanks in advance!
1 Solution
nociSoftware EngineerCommented:
For pop/imap yes.
For smtp no...

It works like this:

assume an address of: someone@target.xx
then the MX DNS RR for target.xx , which specifies which server to use
if successfull the mentioned mail server is used to further handle it. (say the name mail.target.xx is returned)
if it fails, the A DNS RR for target.xx is used for further access.

The receiving mailserver must be configured to ALLOW the reception of mail with either ANY domain name (Open Relay) or just the domain (mail.target.xx).

Only if you can persuade google to allow relaying for you you can send any mail for outgoing and if you can park you domain there you can receive mail for the target.xx address.

The trickiness here is that google wants you to use two different hostnames to access the two protocols you need for mail to work (smtp = sending, imap = receiving).  Currently, you can access both imap and smtp from both hostnames, so if you create a CNAME for mail.ourdomain.com that points to either smtp.googlemail.com or imap.googlemail.com, it will work.  However, the reason google told you to use two different hostnames is that it allows them to separate at some time in the future, which means that in the future, they may do just that and you would need to reconfigure clients to get them working again.

If you're OK with that, here's how I would proceed:

A few days before migration, lower the TTL for mail.ourdomain.com and your MX records to 300 (5 minutes).  This will make the DNS changes propagate throughout the internet much faster.

When you're ready to switch over, delete the A record for mail.ourdomain.com and create a CNAME record for mail.ourdomain.com that points to smtp.googlemail.com.  Within 5 minutes, you should be able to access your new mailboxes on google apps.

To help reduce the amount of work needed if google does separate smtp and imap, I would also create CNAME records for imap.ourdomain.com -> imap.googlemail.com and smtp.ourdomain.com -> smtp.googlemail.com and configure all new clients to use imap.ourdomain.com and smtp.ourdomain.com instead of mail.ourdomain.com.

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