Corrupt HTML messages in Outlook

[Robert B]

We've got a rather odd problem with HTML formatted email in Outlook. It
mainly seems to occur when someone replies to an HTML formatted email in
HTML. The resultant email ends up rather confused with something similar to
the following:

+ADwAIQ-DOCTYPE HTML PUBLIC +ACI--//W3C//DTD HTML 4.0
Transitional//EN+ACIAPg- +ADw-HTML+AD4APA-HEAD+AD4- +ADw-META
http-equiv+AD0-Content-Type content+AD0AIg-text/html+ADs-
charset+AD0-iso-8859-1+ACIAPg- +ADw-META content+AD0AIg-MSHTML
6.00.2800.1528+ACI- name+AD0-GENERATOR+AD4- +ADw-STYLE+AD4AQA-font-face +AHs-
font-family: Sabon+ADs- +AH0- +AEA-page Section1 +AHs-size: 612.0pt
792.0pt+ADs- margin: 72.0pt 90.0pt 72.0pt 90.0pt+ADs- +AH0- P.MsoNormal +AHs-
FONT-SIZE: 12pt+ADs- MARGIN: 0cm 0cm 0pt+ADs- FONT-FAMILY: +ACI-Times New
Roman+ACI- +AH0- LI.MsoNormal +AHs- FONT-SIZE: 12pt+ADs- MARGIN: 0cm 0cm
0pt+ADs- FONT-FAMILY: +ACI-Times New Roman+ACI- +AH0- DIV.MsoNormal +AHs-
FONT-SIZE: 12pt+ADs- MARGIN: 0cm 0cm 0pt+ADs- FONT-FAMILY: +ACI-Times New
Roman+ACI- +AH0- A:link +AHs- COLOR: blue+ADs- TEXT-DECORATION: underline
+AH0- SPAN.MsoHyperlink +AHs- COLOR: blue+ADs- TEXT-DECORATION: underline
+AH0- A:visited +AHs- COLOR: purple+ADs- TEXT-DECORATION: underline +AH0-
SPAN.MsoHyperlinkFollowed +AHs- COLOR: purple+ADs- TEXT-DECORATION: underline
+AH0- SPAN.EmailStyle17 +AHs- COLOR: windowtext+ADs- FONT-FAMILY: Arial +AH0-
DIV.Section1 +AHs- page: Section1 +AH0- +ADw-/STYLE+AD4- +ADw-/HEAD+AD4-
+ADw-BODY vlink+AD0-purple link+AD0-blue+AD4- +ADw-DIV
align+AD0-left+AD4APA-SPAN class+AD0-159012812-

The actual HTML markups are in there but some characters are replaced with a
short string of characters such as +ADwAIQ- for <.

Has anyone seen this problem before?

Thanks in advance

Robert