I spent some time today configuring Postfix so I could send mail from home via .
Verizon, our ISP, blocks port 25 to external domains, forcing all
outgoing mail through their
outgoing.verizon.net exchange server
(Comcast does the same thing). In order to accept mail,
they also require you authenticate with your Verizon username and
password, so I wanted to use an encrypted connection.
For the purpose of this example, our Verizon username is
Verizon password is
YOURPASS, you're running a local Postfix server
mail.example.com for your site at
12345 is a
free local port.
# cat /etc/postfix/main.cf myhostname = mail.example.com relayhost = [127.0.0.1]:12345 smtp_generic_maps = regexp:/etc/postfix/generic smtp_sasl_auth_enable = yes smtp_sasl_password_maps = hash:/etc/postfix/saslpass … # cat /etc/postfix/generic /^jdoe@(.*)$/ firstname.lastname@example.org /^root@(.*)$/ email@example.com # postmap /etc/postfix/generic # cat /etc/postfix/saslpass [127.0.0.1]:12345 firstname.lastname@example.org:YOURPASS # postmap /etc/postfix/saslpass # cat /etc/stunnel/stunnel.conf [smtp-tls-wrapper] accept = 12345 client = yes connect = outgoing.verizon.net:465 # /etc/init.d/stunnel restart # postfix reload
$ echo 'testing 1 2' | sendmail email@example.com
Here's what's going on:
- You hand an outgoing message to your local Postfix, which decides to
send it via port
12345on your localhost (
- Stunnel picks up the connection from Postfix, encrypts everything,
and forwards the connection to port 465 on
- Postfix identifies itself as
mail.example.com(myhostname), and authenticates using your Verizon credentials (
- Because Verizon is picky about the
Fromaddresses it will accept, we use smtp_generic_maps to map addresses to something simple that we've tested.
For the generic mapping, I've used a regexp table, that way I don't have to map a bunch of possible original addresses by hand. By using smtp_generic_maps instead of canonical_maps, we only remap addresses before they head off into the wider world. If we used canonical_maps, we would remap all incoming mail, even mail destined for local delivery.
In case you have trouble with someone blocking your incoming mail, things are a bit trickier. You can always accept mail on different ports (e.g. the submission port 587), with an entry like
submission inet n - n - - smtpd
/etc/postfix/master.cf. However, others will not know which port
you selected, because MX records do not allow you to specify
alternate ports. The more modern SRV record allows this, but
mail systems are old-school and don't support SRV. If you have access
to another external server (whose port 25 isn't blocked), you can
point your MX record at that server, and have it forward mail to you
on your strange port.
For the purpose of this example, the remote host has a public IP of
18.104.22.168, and your local site is
example.com, recieving mail on
port 587. All of the following config files are on the remote host.
# cat /etc/postfix/main.cf … proxy_interfaces = 22.214.171.124 relay_domains = example.com relay_transport = relay:[example.com]:587 …
For futher details (e.g. if you are relaying to more than one target), see the Postfix suggestions for being an MX host for a remote site.