postfix-dockerfile

Postfix w/ forwarding and DKIM on CentOS 7

Usage

Here and in the sections following substitute example.com for your domain.

docker run -d --name postfix -p 25:25 \
-e DOMAIN=example.com \
-e VIRTUAL="forward-me to-here@gmail.com:forward-also to-here@gmail.com" \
-e TRUSTED_HOSTS="127.0.0.1 ::1 192.168.0.0 192.168.1.0" \
dtheus/postfix-dkim

VIRTUAL variable is used to specify contents of /etc/postfix/virtual file, which is used here for email forwarding. Lines are separated by colons (:).

TRUSTED HOSTS variable is used to set entries for /etc/opendkim/TrustedHosts. Entries are separated by spaces( ). By default, it is set to 127.0.0.1 ::1 localhost 172.17.0.0 (default docker network). Obviously, docker run ... -e TRUSTED_HOSTS='...' overrides it, so you should explicitly include default entries if needed. No entries would be added to TrustedHosts if trusted hosts variable is set to empty string.

Notice: no domain supplied for incoming addresses.

OpenDKIM signatures reuse

If you already have a pair of keys you want to reuse, there are two ways to use them inside a container:

ENV variables

...
-e DKIM_KEY="-----BEGIN RSA PRIVATE KEY-----\nAKKAKLDJAAKBgQC9...a9N/123456a1b2c3e4d5==\n-----END RSA PRIVATE KEY-----" \
-e DKIM_TXT="mail._domainkey\tIN\tTXT\t(\"v=DKIM1; k=rsa; \" \"p=adf123...asdf12\" )  ; ----- DKIM key mail for example.com \" \
...

Note: use \n for line breaks, \t for tabs and don't forget to escape quotes.

A shared volume

• Put the key pair to some location of your choice on the host. E.g. /etc/opendkim/keys/example.com/. Selector for this image is not default but mail, so files should be:
  • mail.txt
  • mail.private
• run docker container as mentioned above, but also mount this keys directory of the host:

  ...
  -v /etc/opendkim/keys/example.com:/etc/opendkim/keys/example.com
  ...