Problem with preserving MIME format with Dovecot IMAP and Outlook

Hello,

I have installed Dovecot 2.0.19 on Ubuntu 12.04 LTS.  I have set up a very basic IMAP configuration.  I have two
different laptops running Outlook (one MacOS, one Windows 7) and I have configured both to connect to the
Dovecot service.  My problem is, emails in MIME format that I synchronise from one Outlook client are not
being correctly decoded as MIME messages on the other client.  Instead, the message is rendered in
plaintext, starting with the lines:  This message is in MIME format. Since your mail reader does not
understandthis format, some or all of this message may not be legible.
--B_3426360453_22814Content-type: multipart/alternative;	boundary="B_3426360453_4099"

--B_3426360453_4099Content-type: text/plain;	charset="ISO-8859-1"Content-transfer-encoding: quoted-printable

Can anyone help me understand why this might be happening? 

The output from dovecot -n is:

# 2.0.19: /etc/dovecot/dovecot.conf 
# OS: Linux 3.2.0-26-generic-pae i686 Ubuntu 12.04 LTS 

auth_debug = yes 
auth_verbose = yes
disable_plaintext_auth = no
mail_location = maildir:~/Maildir

passdb {
  driver = pam
}

protocols = " imap"