Major upgrade of mail server

[Plutocrat]

First thing to note is that Ubuntu 18.04 is a Long Term Service release, and will be supported until 2023. So no matter how naggy Ubuntu is, you don't actually HAVE to upgrade at this point. You may disable the prompt if if bothers you: just remove or comment out the relevant file in /etc/update-motd.d/

Now the pressure is off, and you have a bit more time, maybe the best idea would be to build and configure a new server using Ubuntu 20, or any other distro, and then migrate the data over to it with dsync. That affords you an opportunity to test the new config before one final sync, and switching the MX records to point to the new server.

If for any reason you are locked into upgrading the current server, the only advice I can offer from a recent dovecot migration between an Ubuntu 18 server and a Ubuntu 20 server, was that the default SSL settings are considerably improved, which meant that a lot of the clients, who were using ancient versions of Outlook, were unable to connect. I needed to downgrade the security (against my better judgement) in order to let them connect, commenting out the line
# ssl_min_protocol=TLSv1.2
so that it defaulted to TLSv1. You might wish to bear this in mind, although any modern email client won't have any problems.

Good luck!

P.

On 08/07/2021 09.15, Shawn Heisey wrote:
> I have a mail server in AWS that is currently running Ubuntu 18.  Every time I log in, I am reminded that I can upgrade to Ubuntu 20.
> 
> On Ubuntu 18, the dovecot version is 3.3.0-1ubuntu0.3.  On Ubuntu 20, it is 2.3.7.2-1ubuntu3.  Many other packages, probably including the mysql server, would also be upgraded.
> 
> Dovecot and Postfix use a postfixadmin database in mysql for users, and postfix is using dovecot-lda to deliver mail.  I am using managesieve from dovecot on roundcube webmail.  As far as I know, my own user is the only one with sieve scripts actually in use ... and I have a LOT of filters/folders for various mailing lists.
> 
> I've been a little bit terrified of doing an upgrade, because I do have a couple of people using my mail server for real work email and I don't want to disrupt them.
> 
> I'm writing today to find out what are the likely pain points I might encounter when doing this kind of major upgrade, and if there is any helpful information that can help me get through those problems.  I'm hoping that it will go smoothly and everything just works.
> 
> Here's the doveconf -n output:
> https://apaste.info/FUgF
> 
> If I have been silly enough to include sensitive data from the config, I would appreciate a heads up so I know what passwords to change.  I did a quick glance and didn't see anything.
> 
> Thanks,
> Shawn