Help with Web Client

[sixftsix]

I have Open Source Zimbra installed with 50 users on a P4 Xeon 2.8 c/w 4Gb RAM and 2 (Mirrored)36Gb Ultra 160 SCSI. Base OS is Ubuntu 6.10 Server. All was well after the Install and everything worked magnificently for about 3 weeks, until I installed Samba. Now the Zimbra Web Based Client is unable to send. All users Keep getting the error " Message not sent; one or more addresses were not accepted, rejected address: name "
This happens for everyone, no matter who they attempt to send a message to. If they attach from an Outlook or Thunderbird client everything works fine. I am at a loss as to what could have been broken by the sanmba install.