Sloan has html mail support in spam but it is not in
bulk-mail on 4.6. You should remove the -message_type
flag from spam.tcl for the time being.
For reference, here is the comment in the code from
sloan in bulk-mail about message_type:
#mohan's hack to fix the passing of message type for the mail.
+ #Comment: I have to ask Caroline or Andrew if itis ok to change
+ #bulk-mail datamodel to accomodate message_type.
+
+ set extra_headers [util_list_to_ns_set [ns_set get $bulk_mail extra_headers]]
+ set message_type [ns_set get $extra_headers bulk-mail-type]
That, and the relatively limited support for html mail in general meant that the intent was to postpone html email to post 1.0.
