My current mail/web server OS is Linux Mint 18.1 Serena with Mate, based on Ubuntu 16.04.6 LTS Xenial Xerus. It comes to the end of the OS's life in April. Uncharacteristically, I've already begun planning the update. :)
Until now I have rented a dedicated Windows server for web sites, on top of which I have a Hyper-V linux OS with the spec above, originally for mail. I have spent much of the past two years transferring web sites from Windows to linux Apache/PHP with the ultimate goal of dumping windows. Reading threads in this forum I have concluded I will probably go for a VPS for mail and web, possibly two, one for each. Windows, I will probably be stuck with for the next 6-8 months: converting to PHP from ASP is not quick and I have a tendency to tinker.
The question is now: what OS? I used to like Mint but from recent experieince v20 is a cow. Which suggests going to Ubuntu 20 with XFCE. I toyed with Manjaro as a server (I use it as a desktop) but failed to get postfix running satisfactorily.
I dislike the idea that some software on Mint and Ubuntu may have to be snap or flatpack. I see no reason to degrade performance and resources. Whether I would need either on a server (postfix, spamassassin, mySQL (or probably MariaDB), Apache and PHP) I do not currently know. Any hints appreciated.
A third OS has suggested itself this week: Debian. I know little about it and have zero experience of it. Again, for preference, XFCE gui. Would there be a significant learning curve from Ubuntu/Mint to Debian? Is there a better alternative with a low learning curve?