Underscore in sender address

[pascal at symsol.com.au]

I noticed that if a underscore is in the domain part
of the sender address then the email gets bounced
and trails with a Bad protocol error in my log file..

This is the relevant line out of the mail-log:

Oct 22 11:00:24 sgroup postfix/pipe[27765]: 19AE520E6D:
to=<root at host.com>, relay=cyrus, delay=0, status=deferred (SOFT BOUNCE -
data format error. Command output: root: Bad protocol )

and this one is the queue message:

-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
19AE520E6D      575 Wed Oct 22 11:00:24  josef at host_name.gaga.com
                      (data format error. Command output: root: Bad
protocol )
                                         root at host.com

-- 0 Kbytes in 1 Request.

I reproduced that behaviour on several of our servers.
The only reason why I am concerned is that people send us messages
from weird (un)masqueraded domains. I could say thats not really my problem
but if it's solveable then.. happy days.

Does anyone know how to fix that. Maybe I need some escaping or
it could be a postfix problem.. anything.

thanks,

pascal