I just setup 2 postfix hidden services and tried to send email using this method. It didn't work. I can telnet to each server and they seem to be up. However the command substitution smtp_tor is not working. Postfix gives the error:
warning: process /usr/lib/postfix/bin/smtp_tor pid 5513 exit status 1
warning: /usr/lib/postfix/bin/smtp_tor: bad command startup -- throttling
However it works when sending mail to yourself on the same server. I think it is having a name resolution problem. Any ideas on how to fix this?