I've followed this guide to setup an email server with IMAP and SMTP. IMAP is working great, but SMTP doesn't work.
If I try to send a message using telnet:
MAIL FROM: <email@example.com> 250 2.1.0 Ok RCPT TO: <firstname.lastname@example.org> 554 5.7.1 <email@example.com>: Relay access denied
Attempting to login with my mail client (Mail.app on OS X Lion) gives this error in the system log:
postfix/smtpd: warning: my.computer.hostname[184.108.40.206]: SASL PLAIN authentication failed: no mechanism available
The client says "The server rejected the password given."
What can I do to get email relaying working?