Our Zimbra 4.5.6 setup has been working fine since Jul, but one user has been complaining of many emails being bounced.

After finally looking around I can see that there are several emails in /opt/zimbra/amavisd/quarantine.

They all share the same failure issue, ie:

Delivered-To: bad-header-quarantine
X-Amavis-Alert: BAD HEADER Duplicate header field: "Message-ID"

And all the emails have been sent from Microsoft Office 12.0.

Is this a bug with Zimbra or with Outlook? Is there a workaround that I can apply? I presume I could edit the /opt/zimbra/conf/amavisd.conf file and uncomment this line:

# $final_bad_header_destiny = D_PASS;

Thanks in advance.