I'm considering Zimbra for a major deployment (major for me anyway).

First, the situation:

1) 25 locations with each location having between 25 and 100 users, the average being about 50 per location.

2) There will be a total of 20 e-mail domains among those locations.

3) About 1/2 of the users will be HEAVY users (mail, calendar, large attachments, etc.).

4) Some of the locations will want their own Zimbra servers onsite. Others will permit me to host them.

5) Ideally, they'd like to share a common GAL.

6) In a perfect world, they would be able to share calendar functionality as well. For example, someone at location #1 would be able to schedule a meeting with people at locations #4, #7, and #15.

Can these items be accomplished? If so, what's the best path?

If not, where are the problems going to lie?

Now, because Outlook integration, online backup, and support will be important, only the Network version of Zimbra is being considered.