Dkimproxy is a great program for getting Postfix to both sign and validate DomainKeys and DKIM messages. Prior to dkimproxy, one would have used dk-filter and dkim-filter which did DomainKeys and DKIM signing separately. dkimproxy is a newer version that combines the functionality into one program. Installing it can be a bit complicated because it isn’t available in most distro repositories, and requires several Perl modules that need to be installed. Configuring it can be difficult as well, because it involves making changes DNS and postfix, in addition to its own configuration.
I wrote these steps below as I went through a recent installation for a customer
You can install the required Perl modules through the RPM Forge Repository if you have it enabled with the command (Thanks JohnB for mentioning that):
yum install perl-Net-Server perl-Error perl-Mail-DKIM
Otherwise, you can install them manually with CPAN. First install the openssl-devel package (You’ll need it for CPAN to install Mail::DKIM)
yum install openssl-devel
Now install the required Perl modules
# perl -MCPAN -e shell > install Net::Server > install Error > install Mail::DKIM
Download and install the actual dkimproxy code:
cd /usr/local/src wget http://internap.dl.sourceforge.net/sourceforge/dkimproxy/dkimproxy-1.0.1.tar.gz tar -xvzf dkimproxy-1.0.1.tar.gz cd dkimproxy-1.0.1 ./configure --prefix=/usr/local/dkimproxy make make install
You should now have the program installed in /usr/local/dkimproxy. A sample init file is included, so we can copy it into place also:
cp /usr/local/src/dkimproxy-1.0.1/sample-dkim-init-script.sh /etc/init.d/dkimproxy
Create a ‘dkim’ user and group, but lock the password:
useradd -d /usr/local/dkimproxy dkim passwd -l dkim
That should be enough to get dkimproxy running, but it isn’t configured yet.
Create a key file for your domain
cd /usr/local/dkimproxy/etc/ openssl genrsa -out domain.tld.key 1024 openssl rsa -in domain.tld.key -pubout -out domain.tld.pub
Now create a DNS TXT record for mail._domainkey.domain.tld with the contents of domain.tld.pub. Your public key will span at least two lines, so combine all of the lines of the key together when putting it in your DNS record. The whole DNS record will look something like this:
k=rsa; t=s; p=MFwwDQYJ......0JMCAwEAAQ==
(Note that the key is pretty long and I’ve shortened it here)
You could now confirm the key is correct in your DNS:
[root@host etc]# host -ttxt mail._domainkey.domain.tls mail._domainkey.domain.tld descriptive text "k=rsa\; t=s\; p=MFwwDQYJ......0JMCAwEAAQ=="
(Note that the key is pretty long and I’ve shortened it here)
Now tell dkimproxy about the key files, and configuration parameters. Create /usr/local/dkimproxy/etc/dkimproxy_out.conf with this content
# specify what address/port DKIMproxy should listen on listen 127.0.0.1:10027 # specify what address/port DKIMproxy forwards mail to relay 127.0.0.1:10028 # specify what domains DKIMproxy can sign for (comma-separated, no spaces) domain domain.tld # specify what signatures to add signature dkim(c=relaxed) signature domainkeys(c=nofws) # specify location of the private key keyfile /usr/local/dkimproxy/etc/domain.tld.key # specify the selector (i.e. the name of the key record put in DNS) selector mail
And copy the sample inbound config to the real inbound config
cd /usr/local/dkimproxy/etc cp dkimproxy_in.conf.example dkimproxy_in.conf
Now you should be able to start up dkimproxy, and configure it to start at boot:
/etc/init.d/dkimproxy start chkconfig dkimproxy on
And the last step is just to modify the postfix configuration to tell it to forward messages sent to port 587 through dkimproxy for signing. I added these three sections to /etc/postfix/master.cf
### dkimproxy filter - see http://dkimproxy.sourceforge.net/postfix-outbound-howto.html
#
# modify the default submission service to specify a content filter
# and restrict it to local clients and SASL authenticated clients only
#
submission inet n - n - - smtpd
-o smtpd_etrn_restrictions=reject
-o smtpd_sasl_auth_enable=yes
-o content_filter=dksign:[127.0.0.1]:10027
-o receive_override_options=no_address_mappings
-o smtpd_recipient_restrictions=permit_mynetworks,permit_sasl_authenticated,reject
# specify the location of the DKIM signing proxy
# Note: the smtp_discard_ehlo_keywords option requires a recent version of
# Postfix. Leave it off if your version does not support it.
dksign unix - - n - 10 smtp
-o smtp_send_xforward_command=yes
-o smtp_discard_ehlo_keywords=8bitmime,starttls
# service for accepting messages FROM the DKIM signing proxy
127.0.0.1:10028 inet n - n - 10 smtpd
-o content_filter=
-o receive_override_options=no_unknown_recipient_checks,no_header_body_checks
-o smtpd_helo_restrictions=
-o smtpd_client_restrictions=
-o smtpd_sender_restrictions=
-o smtpd_recipient_restrictions=permit_mynetworks,reject
-o mynetworks=127.0.0.0/8
-o smtpd_authorized_xforward_hosts=127.0.0.0/8
If you want it to sign messages sent from the command line sendmail program, modify the pickup service to use the content_filter like this:
pickup fifo n - n 60 1 pickup
-o content_filter=dksign:[127.0.0.1]:10027
Finally restart postfix with ‘postfix reload’, and you *should* have a working installation. You can now use my Domainkeys/Dkim validator to test and ensure that it is working.
Following these instructions works OK, including validator. After ensuring all of the various Postfix ‘pieces’ (amavisd, dkimproxy, greylisting, razor, etc.) work individually, I began to consolidate functions.
My problem today is using dkimproxy when forwarding filtered mail from amavisd via Postfix submission. The complaint is, “warning: proxy 127.0.0.1:10026 rejected “XFORWARD NAME=hosta ADDR=MY.IP.HOST.A PORT=47805 HELO=smtpd.example.com PROTO=ESMTP SOURCE=REMOTE”: “530 5.7.0 Must issue a STARTTLS command first” ” While searching for an answer, found a dkimproxy FAQ suggesting “-o smtpd_use_tls=no” in master.cf After-queue. but that didn’t stop the complaint. Is there another solution?
Flash, it sounds like your configuration is requiring the use of TLS. Take a look in your master.cf for the smtpd process running on port 10026 and remove the line with ‘smtpd_enforce_tls=yes’ if it exists.
Hi Brandon – I’m kinda stuck on the first hurdle – I know nothing about python can you please give me a course of action here – I bow to your unix knowledge I am but a mere windows goof….have also posted to adress given…thanks in advance
root@mail:/usr/local/src/dkimproxy-1.0.1# yum install openssl-devel
There was a problem importing one of the Python modules
required to run yum. The error leading to this problem was:
No module named cElementTree
Please install a package which provides this module, or
verify that the module is installed correctly.
It’s possible that the above module doesn’t match the
current version of Python, which is:
2.5.2 (r252:60911, Apr 21 2008, 11:17:30)
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)]
If you cannot solve this problem yourself, please send this
message to .
No worries,
I finally found the openssl-devel stuff in a package called libcurl4-openssl-dev which was more ubuntu friendly ;¬)
my server is just rebooting – fingers xed
thanks for the article
Johnb.
Johnb – if you don’t have yum working, you have a lot lower level problems. Yum is the package manager for RHEL/CentOS, so you are probably not likely able to update or install *any* packages. Your hosting company, or whoever maintains the server will have to fix that for you, and I’m not terribly familiar with Python myself.
You need gcc on the system to build one of the Mail::DKIM dependencies. Specifically, building of Crypt::OpenSSL::Random (itself a dependency of Crypt::OpenSSL::RSA) fails without gcc.
Cheers
Since I always test sending messages from the command line, I always forget to add this line to the pickup daemon:
http://dkimproxy.sourceforge.net/faq.html#sendmail
@JohnB
Thanks for mentioning that. Most programs now submit things to the smtpd server listening on port 25, but many system administration scripts and CGI programs will use the sendmail command line program which requires this change to /etc/postfix/master.cf:
pickup fifo n - n 60 1 pickup -o content_filter=dksign:[127.0.0.1]:10027I always follow this guide to the letter, with the exception, when using Centos 5, I prefer to install the perl modules from packages on rpmforge. Once you enable rpm forge per:
http://dag.wieers.com/rpm/FAQ.php#B1
You can install these packages:
yum install perl-Net-Server perl-Error perl-Mail-Dkim
I just find it easier to track rpm packages then what’s installed through CPAN.
I use the pickup line to sign mails submitted from thunderbird but my problem is that i use spamassassin too, like this:
smtp inet n – – – – smtpd
-o content_filter=spamassassin
spamassassin unix – n n – – pipe
user=spamd argv=/usr/bin/spamc -e /usr/sbin/sendmail -oi -f ${sender} ${recipient}
When a mail arrives, it goes to spamassassin and after that it is reinjected with sendmail. Therefore it goes to the pickup service and then to the dkimproxy.OUT !! (it was an arraving email)
The mail finally arrives without problems but i don’t like this aditional step and i’m worried about performance…
What can i do?
Cheers
Hi
I followed your tutorial and everything works fine, but when the mail is send through squirrelmail then mail is not signed through DKIMProxy and when the mail is send from the server itself using cli like mail or sendmail command then mail is signed with DKIMProxy. Is there any configuration which I am missing in configuring dkimproxy. I get that message form maillog is
dkimproxy.in[27581]: DKIM verify – none;
What could be wrong.
Thank you
Manish
Manish,
Did you add this line to your master.cf file:
pickup fifo n - n 60 1 pickup -o content_filter=dksign:[127.0.0.1]:10027That is the service used when programs use the command-line sendmail program to submit messages, which is likely what your CLI scripts and squirrelmail use.
Thanks,
Brandon
Hi Brandon,
Thank you for the prompt response, well yes that line is already there in my master.cf file. Squireelmail is using Port 25 for making SMTP connection and maillog gives status as
dkimproxy.in[27581]: DKIM verify – none;
as the mail is send through squirrelmail, also it has dovecot installed with IMAP and POP
So is there something I am missing.
Thank you
Manish
@Manish,
I didn’t think about that correctly. The master.cf file I mentioned above doesn’t sign mail coming in on port 25 (since all inbound mail comes in on that port).
Ideally, you would configure squirrelmail to send to port 587 which should get signed. Alternatively, you could change the ‘smtp’ section of master.cf to look like this:
smtp inet n - n - - smtpd -o content_filter=dksign:[127.0.0.1]:10027That will send all incoming messages through dkimproxy and try to sign them, which obviously adds some un-necessary overhead.
Hi Brandon,
Your suggestions worked perfectly. I changed the SMTP port from 25 to 587 in Squirrelmail configuration and that worked. Thank you for you time and you made a great job by posting this tutorial.
Thank you
Manish
Hi!!!
I have followed the above instructions and as per Email Validation Results of Brandon my mails are properly being singed and verified but still yahoo and hotmail put my mails to Junk folder. Please let me know what could be the reason.
Hi Brandon
I had a lot of perl dependency errors during install on CentOS 5.4. I used CPAN ay first and still couldn’t quiet the errors. Next I tried searching for RPMs online and eliminated some. Finally, I installed DAG and used YUM to install latest versions of MAIL::DKIM and dependencies without errors. Next, I installed dkimproxy 1.2 with success. I followed the configure instructions exactly, setup the init/d script and config files, made the mods to EXIM, and was ready to go. or so I thought. When starting with service dmproxy start I get green lights, but when I check a few seconds later with service dmproxy status I see that both the in and out processes have stopped. Nothing at all in the system logs, so I have nothing to go on.
Any ideas? Is there a switch for debug or verbose logging?
Thanks!
@Tapan,
A working signature does not automatically mean that emails won’t be marked as spam. It just provides a way for them to reliably track your domain’s reputation.
Hi,
I think you have a typo in the following code:
[root@host etc]# host -ttxt mail._domainkey.domain.tls
mail._domainkey.domain.tld descriptive text “k=rsa\; t=s\; p=MFwwDQYJ……0JMCAwEAAQ==”
Shouldn’t it be:
[root@host etc]# host -ttxt mail._domainkey.domain.tld
Hello Brandon,
This is great informaiton. I was able to install dkimproxy on a server running debian 4.0. I still haven’t been abel to get the dkimproxy service to run properly.
When I run:
/etc/init.d/dkimproxy start
everything seems to run fine. But when I check the status with “dkimproxy status” the result are:
dkimproxy.in… stopped
dkimproxy.out… stopped
Any idea why services won’t start? Any help would be appreciated.
@Raul, try taking a look at /var/log/mail.info for any hints as to what is failing.
how would this work with multiple instances on postfix 2.7+
Hi Brandon,
Your tutorial is commendable. I have used SPF validator so many times to check my Domain validation. Now i want to install domain key and dkim on my Debian5 installation.
What perl modules or packages can i get from debian repository to proceed with this installation.
Thank you for your help.
Keep up good work
Hi
I have One SMTP gateway server configured with dkimproxy and the mail sent from that server is getting signed with domainkeys and dkim but when the mail is sent from the relayed server to this server the mails are not getting signed. I have 30 mail nodes and all those nodes are setup to relay mails to the main SMTP gateway. I want all the mails sent by all of those 30 nodes to be signed through SMTP gateway. Any help would be appreciated.
Thanking You,
Hi Brandon,
How I can get mail signed using dkimproxy on SMTP gateway server for which the mails are send from different web nodes to this main SMTP gateway server to deliver it outside the world. Dkimproxy is installed and configured on main server and it’s working fine but doesn’t works when the mails are relayed through that server.
Thanking you,
Manish
@Manish,
You’ll probably need to make a change to master.cf which will send the authenticated messages through DKIMProxy
Hi Brandon
I have already configured dkimproxy for outbound mails and it works fine.
now i need to configure dkimproxy for inbound mails on the same server where dkimproxy running for outbound mails.
Please help me in that,
because i folllowed the instruction given in below URL
i.e. http://dkimproxy.sourceforge.net/postfix-inbound-howto.html
can you please provide me detail information about how to setup dkimproxy for inbound mails or steps
like any free article on internet ,
i followed above mention URL for settingup dkimproxy for inbound mails
Here is the my dkimproxy.in
——————————————
# specify what address/port DKIMproxy should listen on
listen 127.0.0.1:10025
# specify what address/port DKIMproxy forwards mail to
relay 127.0.0.1:10026
Dkimproxy inbound ports seen on server
=====================
tcp 0 0 127.0.0.1:10025 0.0.0.0:* LISTEN 24229/perl
tcp 0 0 127.0.0.1:10026 0.0.0.0:* LISTEN 15399/master
& i successfully achieved, i have seen Dkimproxy inbound ports on my server
is it enough ?
one more thing , please tell me if i am missing anything that are necessary in setup of dkimproxy for inbound mails
And how to verify that your mails are getting signed,
or how to send mail for checking inbound mails
please suggest me because i am new to dkimproxy implementation .
Awaiting for your kind reply
hello,
thank you in advance for thix wonderful tutorial,
i have some problem if you can help me that will be appreciated.
when i try to write that host -ttxt mail._domainkey.domain.tls
this message appears
Host mail._domainkey.domain.tld not found: 3(NXDOMAIN)
thank you in advance..
Hi Brandon,
Thank you soooo much for this great tutorial! I spent many hours trying to get Dkimproxy work until I found this page. Just a single line of code helped me a lot! 🙂
Once again, thank you, and all the best to you!
Nick