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What are the steps for a safe and reliable migration of a mail server from an old hardware to a new one, being changed OS, SW and so on?

Once the new machine is installed, the software is semi-configured what is the best way to replace the old server having the lowest down time ?

Any suggestion is very appreciated, especially keeping into account problems related to SSL certificates, IP address, DNS issues and so on. User account, aliases,and domains migration is not a real problem at the moment instead.

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When changing IPs, I am a BIG fan of running a simple TCP proxy on the old machine for at least a few days. This allows you to get away with stale DNS records around the internet during the switchover. This applies to any service, not just SMTP. Also, you can do things like start the service on the new machine, stop the old service, fire up the tcp proxy, and THEN change the DNS. This way, if you run into problems on the new server, you can just stop the TCP proxy and restart the old service while you fix the new service.

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can you point out a good and simple tcp proxy for debian Gnu/Linux? – drAlberT Nov 6 '09 at 16:50
netcat and inetd. Should be on your system already. – Zimmy-DUB-Zongy-Zong-DUBBY Nov 6 '09 at 18:42

I can't speak for the best solution, but two things helped me to really minimize any kind of downtime.

  • I used a dummy domain to configure the new mail server originally. Got a 1-month free trial certificate and was able to verify incoming/outgoing mail, as well as mail flow between the old & new servers BEFORE any kind of switchover.

(this also let me move mailboxes one at a time to get the activesync users set up individually)

  • On Cutover Day, I simply redirected the external IP entry on our firewall to point from the old server to the new one. No worries about DNS propagation out in the world. Instant switch, and instant undo in case something failed.

After that, it was fairly easy to start stopping services on the old mail server one every few days to make it very easy to isolate problems.

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