On Sat, March 9, 2019 4:53 am, Bill Cole wrote: > On 8 Mar 2019, at 7:33, li...@sbt.net.au wrote:
>> 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. Bill, thank you looking at A record TTLs, they were at 3600, changed to 300 (it seems the idiot who done last DNS never reverted it back to 86400, typical (that's me, of course...)) >> 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. thanks for explaining! makes it simpler. I'll leave Dovecot running but shut down Postfix on old server
