Sorry, but that is not correct. 10.7 Lion was not released until July 2011. Mac Pro 2010 would obviously not have included it, but rather 10.6 Snow Leopard. And again, there is negligible difference between 2009-2010-2012 Mac Pros, such that they all will likely run anything from 10.5 onward through 10.11 equally well (actually 10.12 too even on the 2009s with a firmware update), whether Apple explicitly specified support or not. And I am not running an older system than this machine shipped with, as it shipped with 10.6.
In any case, my difficulty here is not related to OS hardware support or lack of, but rather this version of Dovecot (v1.1) not being able to do separate quotas for separate namespaces. Dovecot v2 might be able to, but there had apparently been difficulties with that as well, from I've read.
FT
On Nov 22, 2016, at 10:31, @lbutlr <kremels@kreme.com> wrote:
On Nov 21, 2016, at 7:34 PM, Fred Turner <fred@c5consulting.net> wrote: Lol, may actually be a 2010...which is essentially no different than a 2012. Mac OS X 10.6.8 would work just fine on that hardware. And probably 10.5.8 as well!
It is generally not possible o install an older OS on a Mac than it shipped with.
That machine, even if it’s a 2010, will run 10.7, 10.8, 10.8, 10.10, 10.11, or even 10.12.
You might have better luck with a support OS.