I recently needed to do some testing with sending mail, and needed a host that would accept mails without asking questions, and just discard it. This turned out to be pretty easy with Postfix.   Starting with a fresh installation on Debian Lenny, add the following to /etc/postfix/main.cf:

# accept all mail
relay_domains = static:ALL
# then get rid of it
smtpd_end_of_data_restrictions = check_client_access static:discard

And before I even got to send a test mail, someone had beat me to it:

Jul  9 03:43:58 mx02 postfix/smtpd[13940]: 6BC681740FC: discard: END-OF-MESSAGE
from 114-45-59-8.dynamic.hinet.net[]: <114-45-59-8.dynamic.hinet.net
[]>: Client host triggers DISCARD action; from=<z2007tw@yahoo.com.tw>
to=<tv9977ccv@yahoo.com.tw> proto=SMTP helo=<>

Yes, I probably should have firewalled out port 25…