On 8 Mar 2019, at 7:33, li...@sbt.net.au wrote:
I have Postfix/Dovecot/Mysql on Centos 7 with mail_version = 3.2.4
setup new server same hostname as old server with mail_version = 3.3.3
using same hostname as old server
the thought was to change A records to point mailserver hostname to
new
server IP at switch over time
is that an OK idea ?
That's how I always do it, and it works well. Make sure you reduce the
TTL value of the A record to a short value for at least twice the normal
TTL before doing the switch. I like to use 300s just to give myself a
slow ramp-up on a new machine that I can watch for trouble, but if you
don't have constant flow you can go as low as 60s before oddball
resolvers show their quirks. So if your current TTL is 86400 (1 day) you
should reduce the TTL and wait 2 days before cutting over. In principle,
1 TTL should work, but in practice, there are weird DNS practices out
there in the wild.
what do I then need to set the old server to forward all mail to new
server ?
The more important question is: WHY?
Shut down Postfix on the old server, start the new server, switch the A
record. The worst that is likely to happen is a handful of sites will
cache the old A too long, try and fail to connect to send a message, and
retry a few minutes later to the new server. The absolute worst possible
effect is if somewhere someone has a hardcoded route for your mail by IP
or a broken MTA that only ever retries deferred messages on the same IP,
their mail to you will fail. Those senders will be accustomed to their
mail being broken on a regular basis...
The risk of leaving the old server up and relaying to the new server is
that the old server may become a clearer path for unwanted email than
directly to the new server.
--
Bill Cole
b...@scconsult.com or billc...@apache.org
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Available For Hire: https://linkedin.com/in/billcole
