rylorin/postfix-relay repository overview

⁠postfix-relay

Postfix SMTP relay docker image. Useful for sending email without using an external SMTP server, or for forward emails for virtual domains.

⁠Usage

docker pull rylorin/postfix-relay or clone and build it yourself. Default postfix is configured not to be an open relay as it has to be exposed publicly on Internet to receive your virtual domains emails.

All postfix configuration options can be set using POSTFIX_<name> environment variables. See Dockerfile⁠ for default configuration. You can use POSTFIX_myhostname to set the FQDN used by 220/HELO.

⁠Using docker run

docker run \
	-e POSTFIX_myhostname=smtp.domain.tld \
	--name smtp \
	rylorin/postfix-relay

⁠Using docker-compose

app:
  # use hostname "smtp" as SMTP server

smtp:
  image: rylorin/postfix-relay
  restart: always
  environment:
    - POSTFIX_myhostname=smtp.domain.tld

⁠SPF

When sending email using your own SMTP server it is probably a very good idea to setup SPF⁠ for the domain your sending from.

⁠DKIM

To enable DKIM⁠ specifying a white space separated list of domains in the environment variable OPENDKIM_DOMAINS. At container start key pairs for each domain will be generated if not found in /etc/opendkim/keys/<domain>. To persist the keys make sure to add a host directory volume for /etc/opendkim/keys. If your using docker-compose it will automatically take care of moving data volumes between container recreates.

DNS records to configure can be found in the container log or by running docker exec <container> cat /etc/opendkim/keys/*/mail.txt.

⁠Virtual domains forwarding

You can set up Postfix to forward all mails coming on your domain email to your other address like gmail.

mail for [email protected] ==> [ site.com Postfix server ] ==> forwarded to [email protected]

⁠DNS settings of domain

First it's necessary to ensure that all mail for your domain will be delivered to your Postfix server. You do that by adding a MX record to your DNS, like:

site.com. 85100 IN MX 10 mail.site.com.

where mail.site.com. is your Postfix server address.

⁠Docker host setting

On your docker host you need to setup a directory which will contains your virtual address mapping file. This directory will be mounted to the docket image and shared with Postfix. Your virtual file should look like:

@site.com			[email protected] [email protected]
[email protected]	[email protected]
@site3.com			[email protected]

Read Postfix documentation for more information.

⁠Docker image setup

Assemble everything using docker-compose:

version: '2'
services:
  app:
    # use hostname "smtp" as SMTP server
  smtp:
    image: rylorin/postfix-relay
    environment:
      POSTFIX_virtual_alias_domains: site.com site2.com site3.com
      POSTFIX_myhostname: mail.site.com
    volumes:
    - /path/to/your/host/conf.d:/etc/postfix/conf.d:rw
    ports:
    - 25:25/tcp

⁠License

postfix-relay is licensed under the MIT license. See LICENSE⁠ for the full license text.