I suspect that the UW imap server must be modifying the message in the process of disentangling the MIME parts.
UW imapd does not modify the message in any way.
However, if you use traditional UNIX format, the mail delivery system may modify the message by inserting ">" in front of any line that starts with "From".
-- Mark --
http://staff.washington.edu/mrc Science does not emerge from voting, party politics, or public debate. Si vis pacem, para bellum.
