OSS license includes mandatory ads (well, logos/badges) and is not permitted to remove this. Any derivative work must contain different but similar badges. The nearest OSI license to this was recently very controversially passed and still isn't this restrictive. This would pretty much preclude the source from evolving on its own should Zimbra close ranks.The OSS version will always be just that, and if it starts to include ads and other functionality that people may not want, the license permits you to edit the source, recompile and bingo, problem gone. That said, I dont see that ever happening.