I am giving a try to Ubuntu server and I have seen that there are two (at least) things weird in comparison with Centos.
1) the most important is an issue in the Postfix "main.conf" file. As there is no line for "smtp_sasl_security_options = noanonymous", it is impossble to connect postfix to an ISP relay. I get a message like "SASL authentication failed; cannot authenticate to server [...]: no mechanism available". I try with "authentication and encryption" and tick and untick "reject anonymous logins", but the only things that happens is the appearance of the "smtpd_sasl_security_options =" line in "main.conf", but this smptD has not the same effect than the smtp equivalent. Is there a mean to automatically activate this line when the user choose to use a relay ? It would avoid to look for hours on google to find the solution for future users.
2) Comparatively to Centos, there are a lot of services whose the state is "unknown" in Bootup and shutdown page. Not really an issue, but not really user friendly.
Thanks to the developpers to the big job on Virtualmin/Webmin
[EDIT] other troubles convinced me to go back to Centos