From November:

We got the mail information for our Rails site, so I reconfigured the mail server. We’re doing a lot of development, and testing mail is much easier when you can send example mail addresses to one bucket of mail. Here’s how I set up the server to redirect everything addressed to @example.org to a test mail address.

First, I set the mail server up for local delivery only, and I confirmed that I could send mail from a local user to another local user account. Then I experimented with rewriting, using virtual_alias_maps to rewrite addresses to a specific account. I confirmed that worked. Then I checked the database to make sure we didn’t have live e-mail addresses, reconfigured the mail server to deliver Internet mail, and crossed my fingers. A few quick tests showed that mail was being delivered as planned – example.org mail routed to our temporary address, everything else delivered normally. We’ll see how this works!

Here’s our /etc/postfix/main.cf

smtpd_banner = $myhostname ESMTP $mail_name
biff = no
append_dot_mydomain = no
readme_directory = no
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
myhostname = domain.goes.here
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = domains.go.here, example.org
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 = smtp
relay_transport = smtp
virtual_alias_maps = hash:/etc/postfix/virtual
inet_protocols = ipv4

And /etc/postfix/virtual:

@example.org change_to_real_email@example.com

Don’t forget to run postmap /etc/postfix/virtual; /etc/init.d/postfix reload after changing /etc/postfix/virtual and your configuration.