with roundup 1.1.1, we can't just use reply to complete a subscription, 
because the sender is the admin, not the bugtracker.
The sender should be changed, or a reply to with the bug tracker email 
adress should be added.
 
FOr now, I have done that:
 
        if not self.client.standard_message([user_props['address']], 
subject,
                body, (tracker_name, tracker_email)):
 
instead of
 
        if not self.client.standard_message([user_props['address']], 
subject,
                body):
 
line 855-856 in roundup/cgi/actions.py, but IMHO, adding a "reply to" in 
the mail would be better.