rsync /old/server new/server ?

[@lbutlr]

On 13 Mar 2019, at 13:25, Shawn Heisey via dovecot <dovecot at dovecot.org> wrote:
> * Shut down postfix and dovecot on both old and new servers.
> * Updated DNS records to point to new address.
> * Ran one final rsync of maildirs from old server to new server.
> * Waited 30 minutes with services on both servers still shut down.
> * Started postfix and dovecot on new server.

Except for the third minute delay, this is exactly what I did. (I brought the new server up as soon as the sync finished, which was only  a few minutes since I'd been syncing frequently. I did leave the OLD server IP offline for awhile after bringing up the new one.

I also did not wait 3 days after lowering the TTL which was set to 1 day. I waited about a day and a half, maybe a bit less.

What you do not want to do is run the two servers at the same time, which is what it sounded like the OP was intending to do.

-- 
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One Hundred Meters, the Mile, the Marathon -- he'd run them all.