Hi Guys I have read a lot of posts regarding this error...I have followed the Perfect Setup for FC4 to the best of my ability, but I am having this error with Postfix. I can use mail perfectly fine on my local network, when I am outside my local network I can receive but not send. I have checked to enable authentication in my mail client, but it doesn't like the username / password, although I know they are correct because they work for receiving. If I do the ehlo localhost thing, the output is as expected as described in the Perfect Setup. 220 XXXXXXX ESMTP Postfix ehlo localhost 250-XXXXXXX 250-PIPELINING 250-SIZE 10240000 250-VRFY 250-ETRN 250-STARTTLS 250-AUTH PLAIN LOGIN 250-AUTH=PLAIN LOGIN 250 8BITMIME This is part of my main.cf: mydestination = /etc/postfix/local-host-names smtpd_tls_auth_only = no smtp_use_tls = yes smtp_tls_note_starttls_offer = yes smtpd_use_tls = yes smtp_tls_session_cache_timeout = 3600s tls_random_source = dev:/dev/urandom smtpd_sasl_local_domain = smtpd_sasl_auth_enable = yes smtpd_sasl_sasl_security_options = noanonymous broken_sasl_auth_clients = yes smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination smtpd_tls_key_file = /etc/postfix/ssl/smtpd.key smtpd_tls_cert_file = /etc/postfix/ssl/smtpd.crt smtpd_tls_loglevel = 1 smtpd_tls_CAfile = /etc/postfix/ssl/cacert.pem smtpd_tls_received_header = yes smtpd_tls_session_cache_timeout = 3600s Can anyone spot anything here or do I need to give you more info?? Thanks in advance!