I've just installed Zimbra Desktop on Xubuntu 11.10 and configured 2 accounts :
1st Account- POP Account - a POP account (non-Exchange server), and
2nd Account - an IMAP account(Exchange server account configured as IMAP).
No issues with receiving the mails for both accounts.
No issues for sendng mails from POP account. (1st Account)
But when I sent mails from IMAP account (2nd Account), I get NDR with "invalid email addresses" error. However, there is no such problem of sending mails when I send from Outlook Web Access, or Outlook (configured as Exchange Account and also Outlook Anywhere (RPC/HTTP).
Please throw light on where I might've gone wrong.