[fetchmail]problems with reverse "banged" Return-Path

Hi

Hopefully someone here can help me out, though I'm not really
sure where the problem lies (remote SMTP, fetchmail or sendmail).

I have problems with mails that have a Return-Path looking like
"host!user" (which mails from a certain POP3-server has). From
what I have understood this is so called reverse ("bang") path,
and was being introduced with RFC 2821 (?).

[me talking POP3 with pop.home.se]
RETR 1
+OK
X-Auth-No:
Return-Path: <e24.ryd.student.liu.se!quite>
Received: from e24.ryd.student.liu.se [130.236.236.24] by smtp1.home.se
        with Novonyx SMTP Server $Revision:   2.74  $; Wed, 29 Aug 2001
        13:57:54 +0200 (ECTD)
[snip]

When fetchmail tries to retrieve this mail (sent from me,
(quite(_at_)e24) to the @home.se-address), I understand this is the
procedure it follows:

INTERACTION WITH RFC 822
       When  trying  to determine the originating address of a
       message, fetchmail looks through headers in the following
       order:
           Return-Path:
           Resent-Sender: (ignored if it doesn't contain an @)
           [snip]

       The originating address is used for logging, and to set
       the MAIL FROM address when forwarding to SMTP.

This is illustrated by the following output from fetchmail,
in wich sendmail barfs:

fetchmail: SMTP> MAIL FROM:<e24.ryd.student.liu.se!quite> SIZE=841
fetchmail: SMTP< 553 5.5.4 <e24.ryd.student.liu.se!quite>...
 Domain name required for sender address e24.ryd.student.liu.se!quite
fetchmail: SMTP error: 553 5.5.4 <e24.ryd.student.liu.se!quite>...
 Domain name required for sender address e24.ryd.student.liu.se!quite
fetchmail: SMTP< 220 LOCALHOST ESMTP Debian Sendmail
 8.12.0.Beta19/8.12.0.Beta19/Debian 8.12.0.Beta19; Wed, 29 Aug 2001
 19:20:46 +0200

(it also tried to send a bounce to the originator (me) with
"RCPT TO: e24!quite", which ofcourse goes bad as well)

So, what is the problem here...

 Is the Return-Path header of host!user invalid?
 Or should fetchmail be able to rewrite it to user(_at_)host?
 Or should sendmail accept host!user?

Fetchmail (version is 5.9.0) rewriting doesn't seem to do any
good.

Thanks in advance for any thoughts put into this..

//