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I recently moved emails for domains that I host to gmail (keeping the @mydomain.com email address). I thought I was doing everything right so no emails would be lost, but this turned out not to be the case.

Firstly I set up a google account with email accounts for the email addresses on my domain.

Then I changed the MX records of my domain to gmail's.

I know that propagation of changes takes some time to take affect across the web. I thought that any email sent during this time would either go to the old email accounts or to gmail. I could then use my hosting's IP address to get emails from the old servers, and move them across to gmail's.

However during the switch I sent myself emails as a test and they never appeared in either email account. What's more I also didn't get any error message saying the email couldn't be delivered.

I really need to know what went wrong so in future I can guarantee to my clients that no emails will be lost in the transfer process. An interruption in service is not ideal, but so long as all emails do eventually get delivered then its acceptable.

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I'll vote for transfer question on ServerFault –  Lazy Badger Feb 12 '12 at 9:00
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1 Answer

Preface

I'm afraid, here isn't a best place to ask such type of questions: in order to get full detailed answer, we have to cover some deep details of DNS and SMTP. It's a problem for local users here, but not (I hope) on ServerFault

Face

You done almost all correctly, I, maybe, only decreaseвd TTL for MX RR before changing data and would wait data-expiration time in order to make "all perfect"

Main problem is "no any response" from SMTP-transactions in your tests. It's extremely bad sign. Maybe you can check now server-log for MTA, which (first) receive message from your MUA (client program) and must route e-mail message to recipient's server? This way you can at least identify, was message transferred from first hop to next and who to ask for more information about the subsequent history (postmaster@ of collector).

Sorry, without smtp-logs I can't say more

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Thank you for your answer. Are you saying that my method should have not resulted in any emails being lost? Thanks –  user793011 Feb 12 '12 at 9:55
    
@user793011 - yes, it seems so. You may to get some time e-mails into both MX, but not lost - lost mail is a serious reason for special investigation (at least for me, as postmaster with strict professional rules) –  Lazy Badger Feb 12 '12 at 10:35
    
My hosting company have said the following: As soon as the MX records are changed, our servers will stop accepting mail for the domain. Some servers may still have the old MX records cached until they expire, though. The expiry time can be reduced by lowering the MX records TTL before making the change, and allowing time for the new TTL to propagate. –  user793011 Feb 12 '12 at 12:50
    
And then this: Reducing the TTL before changing the MX records is the best way to avoid losing emails, and the cluster should bounce mail that isn't hosted with us; it just didn't catch up with the change, in this case. Unfortunately, there is no way to absolutely guarantee no email will be lost or bounce during an MX record change from one provider to another. Reducing the TTL before the changeover should minimise the window when that could happen, though. –  user793011 Feb 12 '12 at 12:50
    
@user793011 - missing bounces drive me nuts –  Lazy Badger Feb 12 '12 at 16:14
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