No, in my case I get a invitation from a external exchange server. eMail attached with a meeting.ics file. The appointment gets correct to zimbra calendar but the Requester eMail address is wrong:
meeting.ics file contains:
ORGANIZER;CN=:MAILTO:user.name@domain.com
zimbra converts this to:
ORGANIZER;CN=null::user.name@domain.com
and this converts to -> "null" <:user.name@domain.com>
:user.name@domain.com should be
user.name@domain.com
cheers Manuel