ekapusta/docker-postfix repository overview

⁠Versatile Postfix Mail Server (marvambass/versatile-postfix)

maintained by MarvAmBass

FAQ - All you need to know about the marvambass Containers⁠

⁠What is it

This Dockerfile (available as marvambass/versatile-postfix) gives you a completly versatile postfix mailserver.

It signs outgoing mails with DKIM by default. You can initially create one Domain with different users with there passwords.

This is not a POP3 or IMAP server, you will get incomming E-Mails in the Maildir format. Read it with less or link a IMAP Server to the volume.

View in Docker Registry marvambass/versatile-postfix⁠

View in GitHub MarvAmBass/docker-versatile-postfix⁠

⁠Environment variables and defaults

• ALIASES
  • optional, no default, example usage: "postmaster:root;john:root;j.doe:root"
• DISABLE_DKIM
  • default: not set - if set to any value the DKIM Signing will be deactivated
• DKIM_CANONICALIZATION
  • default: simple - can be either relaxed or simple
• DISABLE_TLS
  • default: not set - if set to any value TLS will be disabled
• TLS_SECURITY_LEVEL
  • default: may see documentation⁠
• CERT_FILE
  • File with the Postfix SMTP server RSA certificate in PEM format. This file may also contain the Postfix SMTP server private RSA key.
• CERT_KEY
  • Optional. File with the Postfix SMTP server RSA private key in PEM format. This file may be combined with the Postfix SMTP server RSA certificate file specified with CERT_FILE see⁠
• CERT_CA
  • A file containing (PEM format) CA certificates of root CAs trusted to sign either remote SMTP client certificates or intermediate CA certificates. see⁠

⁠Running the Mailserver

This Dockerfile is build to be as versatile as possible. Therefore the startup script takes care of all the important things.

You can easily create a new Mailserver for a domain with several users.

Keep in mind, this is a smtp server only. To read recievied mails you should link a folder inside the conatiner. Otherwise all mails will get lost after you delete your container.

To create a new postfix server for your domain you should use the following commands:

docker run -p 25:25 -v /maildirs:/var/mail \
	-v /dkim:/etc/postfix/dkim/ \
	-e 'ALIASES=postmaster:root;hostmaster:root;webmaster:root' \
	ekapusta/docker-postfix \
	yourdomain.com \
	user:password \
	user1:password \
	user2:password \
	userN:password

this creates a new smtp server which listens on port 25, stores mail beneath /mailsdirs.

The /dkim directory has to contain a DKIM-Key (see above) with the name dkim.key

It has serveral user accounts like user1 with password "password" and a mail address [email protected]⁠

⁠TLS (port 587)

⁠self signed certificate

For generate self signed certificate run

openssl req -new -nodes -x509 -out smtpd.pem -keyout smtpd.pem -days 3650

IMPORTANT: Common Name must contain the fully-qualified host name

For start:

docker run -p 587:587 -v /maildirs:/var/mail \
		-v /dkim:/etc/postfix/dkim/ \
		-v /cert:/etc/postfix/certs
		-e 'CERT_FILE=/etc/postfix/certs/smtpd.pem' \
        -e 'CERT_KEY=/etc/postfix/certs/smtpd.pem' \
        -e 'CERT_CA=/etc/postfix/certs/smtpd.pem' \
		-e 'ALIASES=postmaster:root;hostmaster:root;webmaster:root' \
		ekapusta/docker-postfix \
		yourdomain.com \
		user:password \
		user1:password \
		user2:password \
		userN:password

⁠DKIM

This Server uses DKIM by default. So we need our DKIM Keys. If you don't have a DKIM Key, the Server will generate it on the first start. Just be sure, that you make the directory /etc/postfix/dkim/ available and install the logged public key to your DNS System

⁠More about DKIM

To generate those keys you'll need the opendkim tools

apt-get install opendkim-tools

This generates a new certificate for @example.com with selector (-s) mail. If you want to Test DKIM first, add -t argument which stands for test-mode.

opendkim-genkey -s mail -d example.com

Just put the file mail.private as dkim.key inside the dkim directory you'll later link into the container using -v.

The mail.txt should be imported into the DNS System. Add a new TXT-Record for mail._domainkey [selector._domainkey]. And add as value the String starting "v=DKIM1;..." from the mail.txt file.

Thats all you need for DKIM

⁠Testing SMTP Mail recivieing

$ mailx -r "[email protected]" -s "Test Mail Subject" [email protected] < /etc/hosts

⁠Testing the SMTP Auth and SMTP sending via telnet:

$ echo -ne '\0user\0password' | openssl enc -base64
AHVzZXIAcGFzc3dvcmQ=

$ telnet 127.0.0.1 25
Trying 192.168.4.55...
Connected to yourdomain.com.
Escape character is '^]'.
220 yourdomain.com ESMTP
ehlo test
250-yourdomain.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH LOGIN PLAIN
250 8BITMIME
auth plain AHVzZXIAcGFzc3dvcmQ=
235 Authentication successful
mail from: [email protected]
250 2.1.0 Ok
rcpt to: [email protected]
250 2.1.5 Ok
data
354 End data with <CR><LF>.<CR><LF>
Hi there
this is just a basic test message
.
250 2.0.0 Ok: queued as 2E7FB27F
quit
221 Bye
Connection closed by foreign host.

⁠Links

DKIM Keycheck⁠

DKIM more Infos and signature check⁠