Almost, the virtual hostname is just for easier login purposes etc (so you can visit the box and not type the full @webmail.domain.com part of the email) you'll also need a domain alias (or if already created domain masquerading) : ManagingDomains - Zimbra :: Wiki
-That's not a perfect solution however. One issue would be accepting mail to any address@domain.com (it'll bounce later after it attempts to get to address@webmail.domain.com) but it's better to not even accept.
Long term you should really look at 2 options (after nulling out the alias/catchall/removing the fake domain.)
A) Use the renameDomain command
Code:
zmprov -l rd webmail.domain.com domain.com
Straightforward but do check values for the spam/ham accounts, daily email report address, etc afterwards.
Code:
zmprov gacf | grep webmail.domain.com
(Don't change every value you see in that grep, the server has a hostname of webmail.domain.com afterall, just let us know what you find and we can point you at what to correct.)
B) Create just 'domain.com' as an actual domain on your ZCS box.
Then you can:
-Move users to it.
Code:
zmprov ra user@webmail.domain.com user@domain.com
OR
-Leave user's at user@webmail.domain.com and just create aliases user@domain.com
Code:
zmprov aaa user@webmail.domain.co user@domain.com