I just updated my Ubuntu mail server recipe for Ubuntu 16.04 (https://www.exratione.com/2016/05/a-mailserver-on-ubuntu-16-...). It only took a day of work to find all the holes and fall into them.

Everything core Ubuntu and core mailserver worked fairly well. The standard issue Apache/PHP 7 seems to have some odd kinks around the edges, though - at one point the only thing that worked to make it recognize a newly installed PHP module package was to restart the whole server. I have to wonder if this was something relating to systemd, but I'm not familiar enough yet to tell.

Subsidiary packages had a number of issues, but this is probably just standard PHP ecosystem raggedness at the edges for a new distribution. The Roundcube version installed via package is just outright broken due to bad symlinks, for example.

On the whole I was pleasantly surprised as to how much of a nonissue the transition to systemd was.