PM'd
It's technically possible to change this in the OS edition, but as I understand against the ZPL, so to cut down on everyone doing it...unless bill/john/kevin say otherwise-I'm only providing it upon request.
References-
/forums/installation/7045-customize-url-zimbra.html /forums/developers/3938-changing-url-after-logging.html /forums/developers/3936-changing-url.html
(yes one also points out another method: mod_rewrite...but again your not supposed too...)
It's kinda like the logo re-branding, it's always technically possible; but many modify & forget the 'Zimbra powered' logo, or copyrights, etc. Thus our standard answer has to be: This is a Network Edition feature.
If this changes I'll update you all-or search, it's actually not impossible to find
A) everyone's kinda busy today so I don't have too many people available to ask -which is usually a good thing because it means they got something up their sleeves

B) based on kevin's 3 posts-it seems to be something they want to protect-after all it get's zimbra's name out there
