doc/dkim.md

DKIM

This page is deprecated. DKIM is now by default integrated in YunoHost with [Rspamd](https://rspamd.com)/rmilter.

Note:

• This is the 2nd revision of this Work In Progress How-To activate DKIM and SPF in YunoHost.
• Le DKIM and SPF prevent emails which could be sent with your domain name from a non legitim server. This avoid spam.
• Untill, this is not natively integrated in YunoHost core, it will mean to that Postfix configuration will be blocked (or each time there is a change some configuration lines will need to be added to the end of /etc/postfix/main.cf).
• To be fully functionnal DKIM requires a modification of your DNS zone, which propagantion can take up to 24h.

Sources:

• This tutorial has been initially based on the DKMI section of: http://sealedabstract.com/code/nsa-proof-your-e-mail-in-2-hours/ from Drew Crawford.
• This tutorial has been reviewed based on https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-dkim-with-postfix-on-debian-wheezy from Popute Sebastian Armin

Replace DOMAIN.TLD by your own domain name.

Changes in 2n revision: Much easier to manage more than one DOMAIN.TLD (future proof). Updated configuration as it seemed that the previous one was based on old software.

So, here is the thing:

With a script

Fully automatic script: (single domain)

git clone https://github.com/polytan02/yunohost_auto_config_basic
cd yunohost_auto_config_basic
sudo ./5_opendkim.sh

Manually

We start by installing the right software:

sudo aptitude install opendkim opendkim-tools

Then we configure opendkim

sudo nano /etc/opendkim.conf

Text to be placed in the text file:

AutoRestart Yes
AutoRestartRate 10/1h
UMask 022
Syslog yes
SyslogSuccess Yes
LogWhy Yes

Canonicalization relaxed/simple

ExternalIgnoreList refile:/etc/opendkim/TrustedHosts
InternalHosts refile:/etc/opendkim/TrustedHosts
KeyTable refile:/etc/opendkim/KeyTable
SigningTable refile:/etc/opendkim/SigningTable

Mode sv
PidFile /var/run/opendkim/opendkim.pid
SignatureAlgorithm rsa-sha256

UserID opendkim:opendkim

Socket inet:8891@127.0.0.1

Selector mail

Connect the milter to Postfix:

sudo nano /etc/default/opendkim

Text to be placed in the text file:

SOCKET="inet:8891@localhost"

Configure Postfix to use this milter:

sudo nano /etc/postfix/main.cf

Text to be placed at the end in the text file:

# OpenDKIM milter 

milter_protocol = 2
milter_default_action = accept
smtpd_milters = inet:127.0.0.1:8891
non_smtpd_milters = inet:127.0.0.1:8891

Create a directory structure that will hold the trusted hosts, key tables, signing tables and crypto keys:

sudo mkdir -pv /etc/opendkim/keys/DOMAIN.TLD

Specify trusted hosts:

sudo nano /etc/opendkim/TrustedHosts

Text to be placed in the text file:

127.0.0.1
localhost
192.168.0.1/24
*.DOMAIN.TLD

Create a key table:

sudo nano /etc/opendkim/KeyTable

Text to be placed in the text file: be very careful, it needs to be on a single line for each domain.

mail._domainkey.DOMAIN.TLD DOMAIN.TLD:mail:/etc/opendkim/keys/DOMAIN.TLD/mail.private

Create a signing table:

sudo nano /etc/opendkim/SigningTable

Text to be placed in the text file:

*@DOMAIN.TLD mail._domainkey.DOMAIN.TLD

Now we generate the keys! smile

sudo cd /etc/opendkim/keys/DOMAIN.TLD
sudo opendkim-genkey -s mail -d DOMAIN.TLD

Output the DKIM DNS line to the terminal. Then, we install it on our DNS server. My ZONE file looks like this. (Be very careful with the formatting, the "p=...." needs to be in a single line.)

cat mail.txt

mail._domainkey IN TXT "v=DKIM1; k=rsa; p=AAAKKUHGCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDPFrBM54eXlZPXLJ7EFphiA8qGAcgu4lWuzhzxDDcIHcnA/fdklG2gol1B4r27p87rExxz9hZehJclaiqlaD8otWt8r/UdrAUYNLKNBFGHJ875467jstoAQAB" ; ----- DKIM key mail for DOMAIN.TLD

And we don't forget to put the right rights otherwise opendkim will get grumpy...

chown -Rv opendkim:opendkim /etc/opendkim*

And finally, we restart everything:

sudo service opendkim restart
sudo service postfix restart

To test if it is all working well (don't forget that the DNS propagation can take a bit of take…) you can simply go to mail-tester.com and send an e-mail to the address indicated. Then follow the link and the result will appear.

SPF

Lastly, don't forget to add a SPF key in your DNS zone such as:

DOMAIN.TLD 300 TXT "v=spf1 a:DOMAIN.TLD ip4:<server public IPv4> ip6:<server public IPv6> mx ?all"

As reminder, the SPF field shows that the only machine using the IP address shows in your DNS zone are authorized to send emails. If you don't have IPv6 on your email server, simply delete le ip6:<...> section