Solaris is the most obvious (next new) port on the list
Hello. Just my cents to the discussion. Without any intentions in escalating the OS war, I must say that from a Bussiness perspective, it seems totally weird to me that Solaris has no higher priority as a port.
My points go here:
1) Solaris is considered mature, secure and stable for around 20 years.
2) Althoug open sourced, Solaris still has enormous support options, which makes the leaders/chiefs and and people with responsibllity feel safe when choosing Solaris as production OS.
3) With a Solaris port Zimbra would be considered a serious competitive MS exchange replacer. A status linux will never gain since it still has "garage nerd" status among large companies and non-it-experts. Linux (Debian) is a good product but large Companies would never consider Linux in a production environment. Large companies rely their production on software and services which are backed up, by big and strong companies, which will also exist on the market tomorrow.
4) Solaris has Zones which are a very very fast variation of virtualization. It runs almost at native speed, hence eliminating the security riscs, and make multiple zimbra installations on same physical machine possible.
5) Business -> Earning money... People using/buying Solaris are used to the fact that solid and supported software is not cheap. With that said I personally believe that people already using Solaris don't mind paying for a good mail/exchange solution, as long as they know it is well supported. The point is that porting Zimbra to Solaris will open a huge new market, with companies willing to pay for software and services which can be deployed on Solaris.
Have a nice easter, Best regards, Daniel Mersebak