$ telnet mail.nadir.org 25
Trying 217.114.68.227...
Connected to mail.nadir.org.
Escape character is '^]'.
220 mail.nadir.org ESMTP
helo localhost
250 mail.nadir.org
mail from: foo@nadir.org
250 ok
rcpt to: bar@so36.net
553 sorry, that domain isn't in my list of allowed rcpthosts (#5.7.1)