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Postfix with optional external relays

Simple docker image extending marvambass/versatile-postfix. Based on: https://serverfault.com/questions/660754/mail-sent-from-my-postfix-mail-server-goes-to-gmail-spam

Kubernetes native support

Use Helm Chart do deploy SMTP server to a Kubernetes/OpenShift cluster. Our Helm Chart will automate configuration, data persistence and secrets.

Getting started to use the container

  1. Generate SSL keys if you do not have already any keys (you can use ex. Letsencrypt keys shared from WWW server)
openssl req -new -x509 -extensions v3_ca -keyout ./data/etc/postfix/ssl/cakey.pem -out ./data/etc/postfix/ssl/cacert.pem -days 3650
  1. Run the docker container
version: '2.3'
service:
    smtp:
        image: quay.io/riotkit/smtp:PUT-RELEASE-THERE
        expose:
            - "25"
        volumes:
            - ./data/etc/postfix/ssl/cakey.pem:/etc/postfix/ssl/cakey.pem
            - ./data/etc/postfix/ssl/cacert.pem:/etc/postfix/ssl/cacert.pem
        environment:
            BIFF: no
            SMTPD_BANNER: "RiotKit SMTPD"
            APPEND_DOT_MYDOMAIN: 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
            MYHOSTNAME: localhost
            MYDESTINATION: localhost
            RELAY_HOST: 
            MAILBOX_SIZE_LIMIT: 0
            RECIPIENT_DELIMITER: +
            SASL_AUTH_ENABLE: yes
            TLS_SECURITY_LEVEL: may
            HEADER_SIZE_LIMIT: 4096000
            SMTPD_RECIPIENT_RESTRICTIONS: "permit_mynetworks permit_sasl_authenticated reject_unauth_destination"
            SMTPD_HELO_RESTRICTIONS: "permit_sasl_authenticated, permit_mynetworks, reject_invalid_hostname, reject_unauth_pipelining, reject_non_fqdn_hostname"
            SMTP_SASL_AUTH_ENABLE: yes
            SMTP_SASL_SECURITY_OPTIONS: noanonymous
            DELAY_WARNING_TIME: 4h
            SMTP_USE_TLS: yes
            SMTP_TLS_CA_FILE: /etc/postfix/ssl/cacert.pem
            ENABLE_DKIM: true
            DKIM_CANONICALIZATION: simple
            DKIM_SELECTOR: mail
            ALIASES: 
            

            # The relays are optional, they do not have to be defined
            # all mails could be sent just without any relay
            # redirect all recipient=*@gmail.com mails through gmail account
            RELAY_GMAIL_ADDRESS: [email protected]
            RELAY_GMAIL_PASSWORD: yyy
            RELAY_GMAIL_SMTP_DOMAIN: smtp.gmail.com
            RELAY_GMAIL_SMTP_PORT: 587
            RELAY_GMAIL_EMAIL_DOMAIN: gmail.com

            # the same for outlook
            RELAY_OUTLOOK_ADDRESS: [email protected]
            RELAY_OUTLOOK_PASSWORD: yyy
            RELAY_OUTLOOK_SMTP_DOMAIN: smtp.office365.com
            RELAY_OUTLOOK_SMTP_PORT: 587
            RELAY_OUTLOOK_EMAIL_DOMAIN: your-domain.org

Configuration reference

List of all environment variables that could be used.

- BIFF # (example value: no)

# Banner
- SMTPD_BANNER # (example value: "RiotKit SMTPD")

# With locally submitted mail, append the string ".$mydomain" to addresses that have no ".domain" information. With remotely submitted mail, append the string ".$remote_header_rewrite_domain" instead.
- APPEND_DOT_MYDOMAIN # (example value: no)

# Certificate
- SMTPD_TLS_CERT_FILE # (example value: /etc/ssl/certs/ssl-cert-snakeoil.pem)

# Certificate key
- SMTPD_TLS_KEY_FILE # (example value: /etc/ssl/private/ssl-cert-snakeoil.key)

# Should the SMTPD exposed internally for applications use TLS? Recommended to use.
- SMTPD_USE_TLS # (example value: yes)

# The default is to use the fully-qualified domain name (FQDN) from gethostname()
- MYHOSTNAME # (example value: localhost)

# The list of domains that are delivered via the $local_transport mail delivery transport (defaults to localhost)
- MYDESTINATION # (example value: localhost)

# The next-hop destination of non-local mail; overrides non-local domains in recipient addresses
- RELAY_HOST # (example value: )

# The maximal size of any local(8) individual mailbox or maildir file, or zero (no limit). In fact, this limits the size of any file that is written to upon local delivery, including files written by external commands that are executed by the local(8) delivery agent.
- MAILBOX_SIZE_LIMIT # (example value: 0)

# The set of characters that can separate a user name from its extension (example: user+foo), or a .forward file name from its extension (example: .forward+foo
- RECIPIENT_DELIMITER # (example value: +)

# Enable SASL authentication in the Postfix SMTP client. By default, the Postfix SMTP client uses no authentication (shell client)
- SASL_AUTH_ENABLE # (example value: yes)

# The default SMTP TLS security level for the Postfix SMTP client; when a non-empty value is specified
- TLS_SECURITY_LEVEL # (example value: may)

# The maximal amount of memory in bytes for storing a message header. If a header is larger, the excess is discarded.
- HEADER_SIZE_LIMIT # (example value: 4096000)

# Optional restrictions that the Postfix SMTP server applies in the context of a client RCPT TO command
- SMTPD_RECIPIENT_RESTRICTIONS # (example value: "permit_mynetworks permit_sasl_authenticated reject_unauth_destination")

# Optional restrictions that the Postfix SMTP server applies in the context of a client HELO command
- SMTPD_HELO_RESTRICTIONS # (example value: "permit_sasl_authenticated, permit_mynetworks, reject_invalid_hostname, reject_unauth_pipelining, reject_non_fqdn_hostname")

# Enable SASL authentication in the Postfix SMTP client
- SMTP_SASL_AUTH_ENABLE # (example value: yes)

# Postfix SMTP client SASL security options
- SMTP_SASL_SECURITY_OPTIONS # (example value: noanonymous)

# After sending a "your message is delayed" notification, inform the sender when the delay clears up
- DELAY_WARNING_TIME # (example value: 4h)

# Use TLS in Postfix Client
- SMTP_USE_TLS # (example value: yes)

# Outgoing mailer certificate
- SMTP_TLS_CA_FILE # (example value: /etc/postfix/ssl/cacert.pem)

# DKIM
- ENABLE_DKIM # (example value: true)

# Canonicalization is a process by which the headers and body of an email are converted to a canonical standard form before being signed (values: relaxed/simple)
- DKIM_CANONICALIZATION # (example value: simple)

# To support multiple concurrent public keys per sending domain, the DNS namespace is further subdivided with "selectors". Selectors are arbitrary names below the "_domainkey." namespace. For example, selectors may indicate the names of your server locations (e.g., "mta1", "mta2", and "mta2"), the signing date (e.g., "january2005", "february2005", etc.), or even the individual user.
- DKIM_SELECTOR # (example value: mail)

# /etc/aliases entries @todo: Better examples there
- ALIASES # (example value: )

Adding external relay

To add a relay just define a list of environment variables. You can define as many relays as you want, but for each relay you need to fill all the information as on template below.

This snippet below allows you to route ALL GMAIL recipient mails through your GMAIL account [email protected], the same can be done for other domains and SMTP servers.

[email protected]
RELAY_xxx_PASSWORD=yyy
RELAY_xxx_SMTP_DOMAIN=smtp.gmail.com
RELAY_xxx_SMTP_PORT=587
RELAY_xxx_EMAIL_DOMAIN=gmail.com

Custom main.cf and master.cf

If after mounting main.cf as volume you get a lot of fatal errors such as postconf: fatal: close /etc/postfix/main.cf.tmp: Device or resource busy then you can put your eg. main.cf at /templates/etc/postfix/main.cf.j2 - it's contents will be securely copied to the /etc/postfix/main.cf

The same rule apply for the master.cf.

Developing the container

  • The container is built on quay.io and hub.docker com
  • When you start working on it locally, at first run make develop to install git hooks
  • README.md is automatically generated from README.md.j2, do not edit the generated version!
  • Use make for building, pushing, etc.

Releasing

Just set a tag on git, the container will automatically be built on quay.io and on hub.docker.com

Copyleft

Created by RiotKit Collective, a libertarian, grassroot, non-profit organization providing technical support for the non-profit Anarchist movement.