Alright, so I only got Postfix for a PHP contact form that will send email to a single . I only want it to send out mail to a single external address ([email protected]). I have domain sub1.sub2.domain.com. I installed Postfix out of the Ubuntu repo, with minimal config changes. I cannot get Postfix to send mail externally (though it succeeds for internal accounts, which is unnecessary). The email simply defers if I generate an email using PHP mail(). If I try to form my own in telnet, right after rcpt to: [email][email protected][/email], I get a postfix/smtpd[31606]: NOQUEUE: reject: RCPT from localhost[127.0.0.1]: 550 5.1.1 <[email protected]>: Recipient address rejected: example.com; from=<root@localhost> to=<[email protected]> proto=ESMTP helo=<localhost> when commenting out default_transport = error and relay_transport = error lines, I get the following: Jun 26 14:33:00 sub1 postfix/smtp[12191]: 2DA06F88206A: to=<[email protected]>, relay=none, delay=514, delays=409/0.01/105/0, dsn=4.4.1, status=deferred (connect to aspmx3.googlemail.com[74.125.127.27]:25: Connection timed out) Jun 26 14:36:36 sub1 postfix/smtp[12225]: connect to mta7.am0.yahoodns.net[98.139.175.224]:25: Connection timed out Jun 26 14:38:00 sub1 postfix/smtp[12225]: 22952F88208E: to=<[email protected]>, relay=none, delay=655, delays=550/0.01/105/0, dsn=4.4.1, status=deferred (connect to mta5.am0.yahoodns.net[67.195.168.230]:25: Connection timed out) My main.cf # See /usr/share/postfix/main.cf.dist for a commented, more complete version # Debian specific: Specifying a file name will cause the first # line of that file to be used as the name. The Debian default # is /etc/mailname. #myorigin = /etc/mailname smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu) biff = no # appending .domain is the MUA's job. append_dot_mydomain = no # Uncomment the next line to generate "delayed mail" warnings #delay_warning_time = 4h readme_directory = no # TLS parameters smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key smtpd_use_tls=yes smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache # See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for # information on enabling SSL in the smtp client. myhostname = sub1.sub2.domain.com alias_maps = hash:/etc/aliases alias_database = hash:/etc/aliases myorigin = /etc/mailname mydestination = sub1.sub2.domain.com, localhost relayhost = mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 mailbox_size_limit = 0 recipient_delimiter = + inet_interfaces = all default_transport = error relay_transport = error Also, a dig sub1.sub2.domain.com MX returns: ; <<>> DiG 9.7.0-P1 <<>> sub1.sub2.domain.com MX ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 4853 ;; flags: qr aa rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0 ;; QUESTION SECTION: ;sub1.sub2.domain.com. IN MX ;; AUTHORITY SECTION: sub2.domain.com. 600 IN SOA sub2.domain.com. sub5.domain.com. 2012062915 7200 600 1209600 600 ;; Query time: 0 msec ;; SERVER: x.x.x.x#53(x.x.x.x) ;; WHEN: Fri Jun 29 16:35:00 2012 ;; MSG SIZE rcvd: 84 lsof -i returns empty netstat -t -a | grep LISTEN returns tcp 0 0 localhost:mysql *:* LISTEN tcp 0 0 *:ftp *:* LISTEN tcp 0 0 *:ssh *:* LISTEN tcp 0 0 localhost:ipp *:* LISTEN tcp 0 0 *:smtp *:* LISTEN tcp6 0 0 [::]:netbios-ssn [::]:* LISTEN tcp6 0 0 [::]:www [::]:* LISTEN tcp6 0 0 [::]:ssh [::]:* LISTEN tcp6 0 0 localhost:ipp [::]:* LISTEN tcp6 0 0 [::]:microsoft-ds [::]:* LISTEN