let me explain my problem. I've been using Zimbra for some time, but a client wants to use just the Calendar part of Zimbra. He already has a email server with thousands of users.

The thing is: how I can explain to him that he needs another mail server for Zimbra? Even if he is going to use just the Calendar tool. Is the argument just "because it needs" ?

Can anyone help with a good answer? I think that maybe Zimbra may use his mail server, but I didn't read all the documentation to see if this is an option.

Thanks a lot.