I always see Zimbra mentioned as a good open-source alternative to Gmail. But the demo always made me feel like it was a web-based Outlook UI-wise. Like mbrees

I always see Zimbra mentioned as a good open-source alternative to Gmail. But the demo always made me feel like it was a web-based Outlook UI-wise. Like mbreese, I have wondered for some years if an open-source version of Gmail existed, and also what would be necessary to reproduce the Gmail experience (on the backend side for example, to get to the same speed in search). But I always hear Zimbra which doesn't seem to be the right answer to me.