servers in python

[Max]

I am writing a Hashcash program in python. Rather than create an email 
client plugin, I have done this thru a proxy server which adds the 
Hashcash before forwarding.

What I want to know is whether this is safe. I currently use this code:

class HashcashServer (smtpd.PureProxy):
     def process_message (self, peer, mailfrom, rcpttos, data):
         if peer[0] in trusted_peers:
             # add Hashcash and forward
         else:
             pass

where trusted_peers is a list of peers that are allowed to use the 
service (it is currently just ["localhost"]).

Is there risk of any hacking, or of this becoming an open relay?

--Max