Thanks again, guys. Letsencrypt is working again and Spam is already arriving on the new server (DNS changed, old server with rinetd for IPv4 and Postfix/Dovecot disabled).
I'll watch everything closely for a couple of days and then retire the old server if everthing keeps running fine for the other users too.
Have a nice weekend! 
So far this seems to have gone pretty well with your manual, Nuxwin!
Web Services and i-MSCP are on the new server. The biggest trouble were getting Debian to use MySQL 5.7 instead of MariaDB (and finding/removing Marias leftovers preventing i-MSCP installation) and getting the plugins to work. The toupdate status did not cause the missing dependencies to be installed, instead touninstall, running tasks processer, then from the panel uninstalling those it missed, and reactivating one after the other did the trick.
I do have trouble with the i-MSCP service Lets Encrypt certs though. These were are still present from the old server and linkes to its hostname. If I click renew that won't work because Lets Encrypt expects the validation to be on the old server's hostname. I probably need to remove the existing certs from i-MSCP to have it request new ones instead. How can I do that?
The next thing that gives me a headache is switching the mailserver over. Rsyncing the contents worked well, but my old mailserver is running in dual stack mode and my DNS "mail." records (which is the target of my MX record) A and AAAA currently point to it. The server switch tutorial suggested using rinetd to redirect service requests to the new server. However rinetd does apparently not support IPv6. So if I stop Postfix and Dovecot and just setup the IPv4 redirect (while still having the old IPv6 mail record out there), will this work? Or will it lead to remote servers trying to deliver mails via IPv6 and failing miserably?
Thanks!
Thanks a lot you guys! I'll give it a go in the next couple of days and report back!
Thank you Iceman!
Yes this a private server and there is not terribly much to move. A couple of simple websites, mostly even without databases, some mail accounts with large imap storages and a nextcloud instance. But all in all just for me and my family and I guess taking the long way I'd be done in 30-60 minutes...
Since there has been some trouble with a long broken plugin anyway I'll do it the slow way then and setup the domains anew, import the database contents manually. The only thing I'd like to move 1:1 is the mail data. Does it work to just replace the /var/mail/virtual/* folders once the accounts are setup?
Atm I still have 2 servers in parallel anyway so I guess I'll give it a try and change the DNS records / setup the redirects only if everything was proven successful.
Hi!
In the next couple of days I would like to migrate my i-MSCP installation to a new server. Since my Ubuntu 16.04 occasionally f*cked up updates I would like to run Debian Stretch this time.
After reading many recommendations I was going to follow this manual: https://blog-speedy.de/serverumzug-i-mscp/
Can this be applied across distributions the same way? Are there any other pitfalls to watch for (a buddy said user management of Debian might differ)?
Is this lunacy and I better be staying on Ubuntu altogether?
Thanks for your input 
Ok, thank you Laurent!
Tried dist-upgrading and updated to I-mscp 1.4.6 in the meantime, but of course retrying still fails.
Sure:
Thanks,
Jann
Updating Mailman from 2.0.0 to 2.0.1 fails with
Imscp 1.4.3 on Ubuntu 16.04.2 LTS (GNU/Linux 4.4.0-79-generic x86_64)
Please look into this. If you any additional information just let me know.
Thanks,
Jann
