INSTALL AND CONFIGURE
Install the domain packages:
apt-get install opendkim opendkim-tools
Add the following to /etc/opendkim.conf:
Domain example.com KeyFile /etc/postfix/dkim.key Selector dkim SOCKET inet:8891@localhost
*example.com being your domain
Add the following to /etc/default/opendkim:
SOCKET="inet:8891@localhost"
Add the following to the bottom /etc/postfix/main.cf:
# DKIM # -------------------------------------- milter_default_action = accept milter_protocol = 2 smtpd_milters = inet:localhost:8891 non_smtpd_milters = inet:localhost:8891
Append “no_milters” to the following line in /etc/postfix/master.cf:
-o receive_override_options=no_unknown_recipient_checks,no_header_body_checks
Which becomes:
-o receive_override_options=no_unknown_recipient_checks,no_header_body_checks,no_milters
Now generate the private key and DNS record:
opendkim-genkey -t -s dkim -d example.com
*example.com being your domain
Move the keyfile into place:
mv dkim.private /etc/postfix/dkim.key
Start DKIM and restart Postfix for changes to take effect:
service opendkim start service postfix restart
Now open the dkim.txt file and add the TXT record to your DNS.
Example of record to add:
TXT dkim._domainkey.example.com v=DKIM1; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQC9rulKo58JIb5h+3MMEnYhlnbuVgRoA4w68R/X7qA2Lfv3RpdrrUb+r7KxemIo6PUIOm6uZ5OymhBgpJ0LAWBHBSJjnFmDXNajSgxMOcvkpgmVCW1/k1kxK864WVVSyFVQPyUImqklY+ws4u+mog3PSbuq2J8NFAnvSwzMg3vT1QIDAQAB
*Notice k=rsa; t=y; have been removed as not needed.
TEST
dig dkim._domainkey.example.com txt
*Replace example.com with your domain
Result should be similar to:
dig dkim._domainkey.twitter.com txt ; <<>> DiG 9.8.4-rpz2+rl005.12-P1 <<>> dkim._domainkey.twitter.com txt ;; global options: +cmd ;; Got answer: ;; ->>HEADER< ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;dkim._domainkey.twitter.com. IN TXT ;; ANSWER SECTION: dkim._domainkey.twitter.com. 599 IN TXT "v=DKIM1\; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCrZ6zwKHLkoNpHNyPGwGd8wZoNZOk5buOf8wJwfkSZsNllZs4jTNFQLy6v4Ok9qd46NdeRZWnTAY+lmAAV1nfH6ulBjiRHsdymijqKy/VMZ9Njjdy/+FPnJSm3+tG9Id7zgLxacA1Yis/18V3TCfvJrHAR/a77Dxd65c96UvqP3QIDAQAB" ;; Query time: 34 msec ;; SERVER: 8.8.8.8#53(8.8.8.8) ;; WHEN: Tue Jun 23 10:54:08 2015 ;; MSG SIZE rcvd: 285
Full credit for this post goes to http://www.exratione.com/2014/07/setting-up-spf-and-dkim-for-an-ubuntu-1404-mail-server/
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