I have a client for whom Zimbra appears to solve several problems, but we need to clarify the licensing situation before they go ahead and use it. They are building a commercial subscription-based web application which needs collaboration facilities added to it and are considering using the open source edition because it is likely they will need to make modifications to the source code in order to meet their requirements.

It seems like the terms of the YPL allow them to change the Zimbra source code and expose the resulting functionality to their subscribers for no fee. Their obligations appear to be:

(a) Display the ZimbraInside logo
(b) Submit any source code changes back to Zimbra

Is this correct or am I missing something?

Apologies if this is obvious or has been asked - I just want to be crystal clear on licensing before we/client invest too much effort in Zimbra.

many thanks