This tutorial is part 5 of the mailserver set-up with virtual users and domains using Postfix and Dovecot series. It goes through the steps of installing and integrating OpenDKIM in Postfix on a CentOS 6 Linux VPS.
After completing this tutorial you will end up having OpenDKIM adding digital signatures to your emails, thus making the mailserver set-up even more robust and professional.
Also, learn how to do this on a Debian Squeeze Linux VPS: Install and Configure openDKIM on Debian Squeeze.
What is OpenDKIM?
It is a digital email signing/verification technology, which is already supported by some common mail providers. In general, DKIM means digitally signing all messages on the mail server to verify the message was actually sent from the domain in question and was not spam
UPDATE THE SYSTEM
Before going any further, make sure you’re in a screen session and your system is fully up-to-date by running:
## screen -U -S opendkim-screen ## yum update
ENABLE EPEL REPOSITORY
OpenDKIM is available in the EPEL repository, so we need to enable it on the system before we can install OpenDKIM
## wget -P /tmp http://mirror.pnl.gov/epel/6/i386/epel-release-6-8.noarch.rpm ## rpm -Uvh /tmp/epel-release-6-8.noarch.rpm ## rm -f /tmp/epel-release-6-8.noarch.rpm
INSTALL OPENDKIM
Install the package using yum:
## yum install opendkim
CONFIGURE OPENDKIM
The next thing to do is to configure OpenDKIM. Its main configuration file is located in /etc/opendkim.conf, so before making any changes create a backup and add/edit the following:
## cp /etc/opendkim.conf{,.orig}
## vim /etc/opendkim.conf
AutoRestart Yes AutoRestartRate 10/1h LogWhy Yes Syslog Yes SyslogSuccess Yes Mode sv Canonicalization relaxed/simple ExternalIgnoreList refile:/etc/opendkim/TrustedHosts InternalHosts refile:/etc/opendkim/TrustedHosts KeyTable refile:/etc/opendkim/KeyTable SigningTable refile:/etc/opendkim/SigningTable SignatureAlgorithm rsa-sha256 Socket inet:8891@localhost PidFile /var/run/opendkim/opendkim.pid UMask 022 UserID opendkim:opendkim TemporaryDirectory /var/tmp
SET-UP PUBLIC/PRIVATE KEYS
Generate a set of keys for your mydomain.com domain name:
## mkdir /etc/opendkim/keys/mydomain.com ## opendkim-genkey -D /etc/opendkim/keys/mydomain.com/ -d mydomain.com -s default ## chown -R opendkim: /etc/opendkim/keys/mydomain.com ## mv /etc/opendkim/keys/mydomain.com/default.private /etc/opendkim/keys/mydomain.com/default
add mydomain.com to OpenDKIM’s key table by adding the following record in /etc/opendkim/KeyTable
default._domainkey.mydomain.com mydomain.com:default:/etc/opendkim/keys/mydomain.com/default
next, edit /etc/opendkim/SigningTable and add the following record to OpenDKIM’s signing table:
*@mydomain.com default._domainkey.mydomain.com
and add your domain and your hostname as trusted hosts in /etc/opendkim/TrustedHosts:
127.0.0.1 mydomain.com host.mydomain.com
assuming the domain in question is ‘mydomain.com’ and the server’s hostname is set to ‘host.mydomain.com’
finally, edit your mydomain.com DNS zone and add the TXT record from /etc/opendkim/keys/mydomain.com/default.txt
default._domainkey IN TXT ( "v=DKIM1; k=rsa; "
"p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDApHRr7ZmXRaAB+RQRbP4VdMwIrIHIP18KFtXRsv/xpWc0Gix6ZXN13fcG03KNGKZo2PY+csPkGC5quDnH5V0JEhDZ78KcDWFsU6u4fr9ktVAdt6P7jWXjcyqdHOZ8+YN4cAeU4lRFNgQvdupIcByYwzPYMgBFHfJm9014HvRqhwIDAQAB" ) ; ----- DKIM key default for mydomain.com
it is also a good idea to add an SPF record if you haven’t already
mydomain.com. 14400 IN TXT "v=spf1 a mx ~all"
you can verify your dkim TXT record is valid using dig for example:
## dig +short default._domainkey.mydomain.com TXT "v=DKIM1\; k=rsa\; " "p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDApHRr7ZmXRaAB+RQRbP4VdMwIrIHIP18KFtXRsv/xpWc0Gix6ZXN13fcG03KNGKZo2PY+csPkGC5quDnH5V0JEhDZ78KcDWFsU6u4fr9ktVAdt6P7jWXjcyqdHOZ8+YN4cAeU4lRFNgQvdupIcByYwzPYMgBFHfJm9014HvRqhwIDAQAB"
CONFIGURE POSTFIX
In order to integrate OpenDKIM with Postfix we need to add the following few lines in /etc/postfix/main.cf:
smtpd_milters = inet:127.0.0.1:8891 non_smtpd_milters = $smtpd_milters milter_default_action = accept milter_protocol = 2
(RE)START SERVICES
Add OpenDKIM to your system’s start-up and start opendkim and restart postfix using the following commands:
## service opendkim start ## chkconfig opendkim on ## service postfix restart
TEST THE SET-UP
To test the set-up simply send an email to check-auth@verifier.port25.com and you should receive back an email containing something like this:
========================================================== Summary of Results ========================================================== SPF check: pass DomainKeys check: neutral DKIM check: pass DKIM check: pass
Implementing OpenDKIM to the mailserver set-up with virtual users and domains using Postfix and Dovecot adds another nice feature that makes your emails digitally signed.
But still, there are other features missing like using dovecot sieve rules to filter emails on the server-side, scanning emails for viruses, etc. In the next few related articles, we will be adding additional features to the set-up so stay tuned.
Of course, if you are one of our Linux VPS Hosting customers, you don’t have to do any of this, simply ask our admins, sit back and relax. Our admins will set this up for you immediately.
PS. If you liked this post please share it with your friends on the social networks using the buttons on the left or simply leave a reply below. Thanks.
Great tutorial!
But.. just a question about the test. How can be possible that dkim appears as passed, but DomainKeys check appears as neutral?
DomainKeys are not the same as DKIM, although very similar.
One of the most thorough installation walkthroughs I have ever seen; nothing was left to chance with your instructions. Thanks! You guys should set up a wiki with this and other stuff…
First of all, thank you for your walkthrough
I use Godaddy to change my DNS ZoneFile, and even though I followed your walkthrough I still got a failed result for DKIM saying that the signature could not be verified. Any ideas how I could possibly fix that?
You check that your emails are being authenticated and that your DNS records are properly set up using one of the following testing services:
Send a signed email to sa-test@sendmail.net
Or, send a signed email to check-auth@verifier.port25.com
Great tutorial, thanks!
Great tutorial, thanks!
But I want to ask you is how to configure DomainKeys check: pass
Hi Fxbalacon,
may we ask why you need DomainKeys if you have DKIM working?
DomainKeys Identified Mail (DKIM) is the successor to Yahoo’s DomainKeys. They are quite similar in functionality, except that DKIM has additionally adopted aspects from additional Mail Standards, it is more flexible and secure, it supports multiple signature algorithms (as opposed to just one available with DomainKeys), it has the ability to support signature timeouts in DNS and a few more useful options…
So, you don’t really need DomainKeys if you have DKIM set-up on your mail server.
thanks
finally, edit your mydomain.com DNS zone and add the TXT record from /etc/opendkim/keys/mydomain.com/default.txt
WHERE TO DO THIS? IN WHAT FILE? I DONT GET IT
Each domain have authoritative DNS servers that publish information about that domain. You may use the ‘host -t ns mydomain.com’ command to identify the DNS servers responsible (authoritative) for your domain’s zone file.
If you didn’t change the authoritative name servers for your domain at your domain registrar at the time of registration or later any time, most likely you use your domain registrar’s name servers so you can create a new TXT domain record for your domain via your domain registrar. Log in to your domain registrar, find the ‘DNS Zone Editor’ (or the section where you can create a DNS record) and create a new TXT DNS record.
If you use custom name servers for your domain, you need to edit the DNS zone file hosted at your name servers.
hello.
I installed a new mail server according to your instructions. but SquirrelMail does not receive mail. Can you show me how to solve this problem?
thank you very much!
Did you check your mail server log files?
i did all the things as said but when see email header which received from server it does not show DKIM value
Will Be Glad if Any one Can Help
Did you follow the instructions closely?
Please check your mail server log files for error messages related to DKIM or so.
SPF check: pass
DomainKeys check: neutral
DKIM check: neutral
Sender-ID check: pass
SpamAssassin check: ham
please how can i enable everything is pass
----------------------------------------------------------DKIM check details:
----------------------------------------------------------
Result: fail (signature doesn't verify)
ID(s) verified:
Canonicalized Headers:
date:Tue,'20'17'20'Nov'20'2015'20'09:59:01'20'+0200'0D''0A'
from:ugur@multihome.com'0D''0A'
to:check-auth@verifier.port25.com'0D''0A'
subject:=?UTF-8?Q?=28Konu_Belirtilmemi=C5=9F=29?='0D''0A'
dkim-signature:v=1;'20'a=rsa-sha256;'20'c=relaxed/simple;'20'd=multihome.com;'20's=default;'20't=1447747141;'20'bh=frcCV1k9oG9oKj3dpUqdJg1PxRT2RSN/XKdLCPjaYaY=;'20'h=Date:From:To:Subject;'20'b=
Canonicalized Body:
'0D''0A'
DNS record(s):
default._domainkey.multihome.com. 86024 IN TXT "p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCl+bUxiRBLFqU6yyfkCLQJNlaJxhknhceeXTIxXO1lsTMZHrpddrGSqITgqjY0LzYjUAMvV66vAolgrRTckn8z98+PJI4xXsrMOoi6tjCBem4O+FnVCvGNWRpy7JThxTe2gkUEvTuQ+r0IglaGSfpvmci2IQNaj642bmg5JKgmmQIDAQAB;"
Public key used for verification: default._domainkey.multihome.com(1024 bits)
NOTE: DKIM checking has been performed based on the latest DKIM specs
(RFC 4871 or draft-ietf-dkim-base-10) and verification may fail for
older versions. If you are using Port25's PowerMTA, you need to use
version 3.2r11 or later to get a compatible version of DKIM.
There is no DNS record found for default._domainkey.multihome.com. Please follow the instructions closely to install and integrate DKIM.
Hi,
They are all working: SPF, DKIM, DMARC, DomainKeys and passes all the post25 tests but emails are delivered in SPAM folder only in Gmail.
Here are the headers:
Delivered-To: testpds2@gmail.comReceived: by 10.194.163.39 with SMTP id yf7csp377905wjb;
Thu, 10 Dec 2015 01:15:52 -0800 (PST)
X-Received: by 10.28.4.212 with SMTP id 203mr41790134wme.89.1449738952207;
Thu, 10 Dec 2015 01:15:52 -0800 (PST)
Return-Path:
Received: from s17772156.onlinehome-server.info (s17772156.onlinehome-server.info. [217.160.108.200])
by mx.google.com with ESMTPS id v10si17523219wjx.223.2015.12.10.01.15.51
for
(version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
Thu, 10 Dec 2015 01:15:52 -0800 (PST)
Received-SPF: pass (google.com: domain of info@pixeldraw.net designates 217.160.108.200 as permitted sender) client-ip=217.160.108.200;
Authentication-Results: mx.google.com;
spf=pass (google.com: domain of info@pixeldraw.net designates 217.160.108.200 as permitted sender) smtp.mailfrom=info@pixeldraw.net;
dkim=pass header.i=@pixeldraw.net;
dmarc=pass (p=QUARANTINE dis=NONE) header.from=pixeldraw.net
Received: from webmail.pixeldraw.net (s17772156.onlinehome-server.info [127.0.0.1])
by s17772156.onlinehome-server.info (Postfix) with ESMTPA id 933451FED
for ; Thu, 10 Dec 2015 10:15:51 +0100 (CET)
DKIM-Filter: OpenDKIM Filter v2.10.3 s17772156.onlinehome-server.info 933451FED
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=pixeldraw.net;
s=mail; t=1449738951;
bh=WkU5qDAu4noB4+ddfOTFnqQoF0uglLhffSImzgEOX4Y=;
h=Date:From:To:Subject;
b=WTQrbxctluSHhg89lCIXmcNXxAtsbqN0qdOV8SyaDFtHSYV+a0LVz4yGpLohSyCHT
KQ2pfAqy8bIPMycFshCv6dEcG54b6lp/GoNfGNL989JfvoN9ffzFho06OQfMD8+H3l
F/dpQAeU2tXVN/JxiKMctrWA4NqmlLDw/JWtxMK8=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8;
format=flowed
Content-Transfer-Encoding: 8bit
I think the problem is: “Received: from webmail.pixeldraw.net (s17772156.onlinehome-server.info [127.0.0.1])
by s17772156.onlinehome-server.info (Postfix) with ESMTPA id 933451FED”
127.0.0.1???
Thanks in advance
Please run:
cat /etc/hosts
and provide us with the output.
Hello,
I am having some trouble. Please help if there are anyone. I’ve configured everything just like this. Dkim is working fine if I send email with roundcube webmail. But if I use any external email software then it doesn’t show any dkim record. Can anyone help me?
That’s because your external email client uses your IP to send mail through your SMTP server and an entry needs to be added for your IP or IP range(if your IP is dynamic) in /etc/opendkim/TrustedHosts.
no signing table match for test@example.co
Having this error
Did you setup plublic/private keys for example.co and add the domain to the OpenDKIM’s configuration files ?
Hi.
Thanks for your great tutorial. I made all the things (I think I did this quite correctly) but, when I send a mail to auth-results, here is the answer
SPF check: pass
DKIM check: none
SpamAssassin check: ham
This might be bad for me as no DKIM was found? Ham for SpamAssassin = I’m a spammer, right? What is my mistake? Thanks for the help.
Hi Thibaut,
Our tutorial is tested and it is working without a problem. Please make sure that you closely followed the steps and updated all paths, domains, usernames, etc… accordingly.
I have some problems to configure the domain I think. The webmail works (but no DKIM) but I can’t use Thunderbird to send mails, only IMAP is working… It might be the origin of the problems.
Please check your mail server log files
I have problem not authenticated but DKIM verification successful and no signing table match but DKIM verification successful
Please check your mail server log files.
Great instructions! Worked first time!
dig +short default._domainkey.example.com TXT show nothing