DNS/SPF

Setting up SPF + DK + DKIM with Postfix

• https://matoski.com/article/spf-dk-dkim-plesk-debian/

Shows up a detailed process on how to set up SPF + DK + DKIM with Postfix in Plesk 11.5 on Debian Wheezy, step by step, and how to test to make sure everything is working correctly

I leased a dedicated server from Hetzner, and I got the Plesk option, for administration, so I don’t have to bother with administration, but turns out I’m not so lucky, I’ve ran into a lot of issues with using Plesk, so I had to do my own fixes.

So let’s take a look at how we can integrate SPF + DK + DKIM with Postfix in Plesk 11.5 on Debian Wheezy.

First things, first, if you are using QMail switch to Postfix, to install Postfix you can either use the GUI, or you can do it from a console.

Here is how to do it from the console.

/usr/local/psa/admin/sbin/autoinstaller --select-release-current --install-component postfix

SPF

Let’s open the DNS Template, you will see there that, there is an entry for SPF

v=spf1 +a +mx -all

This means the SPF is enabled on our domain.

Let’s modify it a little bit to be better, if you are gonna host multiple domains from your server, then you should probably modify it too.

v=spf1 +a +mx +ip4:<ip.mail> ?all* <ip.mail> - Is the IP of the mail server that is responsible for sending the mails, it is automatically filled in when you apply the zones

After you do this modification you should apply it

So now my configuration looks like this:

"SPF DNS Template"

Now let’s check with dig if the SPF is OK.

dig myserverplace.de TXT @ns1.myserverplace.de

You will see in the Answer section I have the following entry

myserverplace.de. 600 IN TXT "v=spf1 +a +mx +ip4:144.76.163.46 ?all"

So everything is ok, next onto DomainKeys

DomainKeys

First let’s activate DomainKeys, take a look at the screenshot, and compare my options with yours.

"Plesk Panel DK Enabled"

Ok, now that this has been enabled, let’s go and enable for the domain in question, if it was already checked, uncheck it press OK, and then check it again and press OK, this is so it will regenerate the DomainKeys data in the DNS zone, as I’ve had some problems with the data not present in the DNS zone file

"Enable DK Domain"

OK, now let’s see if the correct data is there, usually it takes a long time for DNS to propagate between 24-48h, there is a simple way to test if the data is there, by querying the Nameserver that hosts your DNS zone, in my case I host my own Nameserver

dig _domainkey.myserverplace.de TXT @ns1.myserverplace.de

You will see in the Answer section I have the following entry

_domainkey.myserverplace.de. 600 IN TXT "o=-"

Now let’s see if the DomainKey is there too

dig default._domainkey.myserverplace.de TXT @ns1.myserverplace.de

In the Answer section you should see something like

default._domainkey.myserverplace.de. 600 IN TXT "p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDAruBNqdsSCKBLwMrFNNKH8z0e7zmlAic7iRoJsDDJK3IlnW8j6G/T6a93m+jqYc6R38MBAZbeSv2LQJ0SepJEsr4Iqk41WFXPBKnyXReO1RXPW5/YnRe6dpJMEqsmPpl2TjInY7ve/6VCiVDOHn9RRrdB+x7CGeK2crgqSZVlFwIDAQAB\;"

As you can see everything is in place now for DomainKeys to work, now let’s continue on to DKIM

DKIM (DomainKeys Identified Mail)

As always lets update the system first

aptitude update
aptitude safe-upgrade

Now we need to install the DKIM filter, or as it’s called now OpenDKIM, for full specification take a look at their site.

aptitude install opendkim opendkim-tools

Now we need to create the necessary folders so OpenDKIM can work proplery

mkdir -pv /etc/opendkim/keys
chown -Rv opendkim:opendkim /etc/opendkim
chmod go-rwx /etc/opendkim/*

This will create the directory where we will hold the keys for OpenDKIM, after this step let’s take a look at how the process will look like, so we can create a script to automate this.

mkdir -p /etc/opendkim/keys/myserverplace.de
cd /etc/opendkim/keys/myserverplace.de
opendkim-genkey -d myserverplace.de -s mail
chown -Rv opendkim:opendkim /etc/opendkim/keys/myserverplace.de
chmod -v u=rw,go-rwx *

This easily understandble, what happens here.

Now you have two files /etc/opendkim/keys/myserverplace.de

ls -lah /etc/opendkim/keys/myserverplace.de
total 16K
drwxr-xr-x 2 opendkim opendkim 4.0K Oct 9 18:43 .
drwxr-xr-x 5 opendkim opendkim 4.0K Oct 9 19:39 ..
-rw------- 1 opendkim opendkim 887 Oct 9 18:43 mail.private
-rw------- 1 opendkim opendkim 303 Oct 9 18:43 mail.txt* /etc/opendkim/keys/myserverplace.de/mail.private

contains the RSA PRIVATE KEY* /etc/opendkim/keys/myserverplace.de/mail.txt

Contains the record you need to add to your DNS zone

Next set is to setup the key tables, signing tables, and trusted hosts

First let’s prepare the files

touch /etc/opendkim/KeyTable
touch /etc/opendkim/SigningTable
touch /etc/opendkim/TrustedHosts* /etc/opendkim/TrustedHosts

needs to contain some data before we continue, so add the following information to this file, and adjust accordingly

127.0.0.1
localhost
144.76.163.46
144.76.163.57
ns1.myserverplace.de
ns2.myserverplace.de
myserverplace.deSo let’s see what does what:* /etc/opendkim/KeyTable

KeyID Domain:Selector:PathToPrivateKey* /etc/opendkim/SigningTable

• The filter used is programmed to read the table by looking for matched domain
• /etc/opendkim/TrustedHosts

It will list the top trusted hosts as you desire

Those three files contain all the necessary information for the signing to work.

So in my case for my domain I do.

echo "myserverplace.de myserverplace.de:mail:/etc/opendkim/keys/myserverplace.de/mail.private" >> /etc/opendkim/KeyTable
echo "*@myserverplace.de myserverplace.de" >> /etc/opendkim/SigningTable
echo "myserverplace.de" >> /etc/opendkim/TrustedHosts
echo "mail.myserverplace.de" >> /etc/opendkim/TrustedHosts

So let’s put all this together in a script so we don’t have to do it all the time

#!/bin/bash
# /opt/generatedkim.sh
die () {
echo >&2 "$@"
exit 1
}

[ "$#" -eq 1 ] || die "1 argument required, $# provided, domain required, ex: ./script example.com"

cwd=`pwd`
opendkim="/etc/opendkim"
location="$opendkim/keys/$1"
[ -d "$location" ] && die "There is already a directory in the folder, delete the folder if you want to create a new one"

mkdir -p "$location"
cd "$location"
opendkim-genkey -d $1 -s mail
chown opendkim:opendkim *
chown opendkim:opendkim "$location"
chmod u=rw,go-rwx *
echo "$1 $1:mail:$location/mail.private" >> "$opendkim/KeyTable"
echo "*@$1 $1" >> "$opendkim/SigningTable"
echo "$1" >> "$opendkim/TrustedHosts"
echo "mail.$1" >> "$opendkim/TrustedHosts"
echo
echo "Put this in the DNS ZONE for domain: $1"
echo
cat "$location/mail.txt"
echo
cd "$cwd"

So if we run the script, we should get output like this, and this is the data we need to put in the DNS zone.

/opt/generatedkim.sh test.de

Put this in the DNS ZONE for domain: test.de

mail._domainkey IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDPzE0GmvFwAQsgcFzopy4zMNWUbL6JM5XIyjBy3bUnANI5axeb/Lw/GBjUoSFLEiO80Tt8m3A5YrBKcodRQQURYiW6/YtElhLupHyfcxQhfNLU4z9JUOJKPjcpMZCj0Xv873QgVOl+7U605JdBHSPOx4ybBZwDq68cw9YFYRPmEwIDAQAB" ; ----- DKIM key mail for test.de

Unfortunatly I don’t have time to create a script to do this automatically, you can always insert a record in MySQL database so it’s in the ZONE and you can regenerate the DNS Zone from the command line, and I won’t be having a lot of domains, so I can add this entry manually to a domain I want DKIM enabled

Let’s open the domain and go to DNS Settings, and you can click ** Add Resource **

You popuplate the following data in the inputboxes* Record type

TXT* Domain name

mail._domainkey* TXT Record

In the text record you copy a part of the contents from the file /etc/opendkim/keys/myserverplace.de/mail.txt, it data should start from v=DKIM1; k=rsa; to the end, without the quotes as you can see it’s in quotes.

In the example above for domain test.de you add only the following contents in the input box

v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDPzE0GmvFwAQsgcFzopy4zMNWUbL6JM5XIyjBy3bUnANI5axeb/Lw/GBjUoSFLEiO80Tt8m3A5YrBKcodRQQURYiW6/YtElhLupHyfcxQhfNLU4z9JUOJKPjcpMZCj0Xv873QgVOl+7U605JdBHSPOx4ybBZwDq68cw9YFYRPmEwIDAQAB

"DKIM Add DNS Zone"

Well that’s it for this, now let’s check with dig if the record is there

dig mail._domainkey.myserverplace.de TXT @ns1.myserverplace.de

You will see in the Answer section I have the following entry

mail._domainkey.myserverplace.de. 600 IN TXT "v=DKIM1\; k=rsa\; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDMziMcgPTWK0kSUKxrgHHzEiWxNkZ2/M0Ugyr/8H9WtoCsJUM+Bc1C9VwqJ6yjTidecDrX7aL0lFZ9Mylku/wtSiPw6KLxMg2LG2vrMzlPTB2lmJNmg/EOu3KPC8BtAuOhXfwVH/ttQbzdKJKWqiCJn7jhF5oqEKnOCORxOQXKIwIDAQAB"

Well everything is setup up at least from the DNS side, now we need to configure Postfix to use this data and sign the emails.

You can also use the following URLs to check the validity of your key* dkim-key-checker

• DKIM Core Tool

In the selector fields try with both mail, and default, you shold be getting valid results

OpenDKIM

We need to edit the configuration file to configure DKIM, open /etc/opendkim.conf with your favorite editor and add the following lines to the end of the file

# Enable Logging
Syslog yes
SyslogSuccess yes
LogWhy yes

# User mask
UMask 002

1. Always oversign From (sign using actual From and a null From to prevent malicious signatures header fields (From and/or others) between the signer and the verifier)

OversignHeaders From

1. Our KeyTable and SigningTable

KeyTable refile:/etc/opendkim/KeyTable
SigningTable refile:/etc/opendkim/SigningTable

1. Trusted Hosts

ExternalIgnoreList /etc/opendkim/TrustedHosts
InternalHosts /etc/opendkim/TrustedHosts

1. Hashing Algorithm

SignatureAlgorithm rsa-sha256

1. Auto restart when the failure occurs. CAUTION: This may cause a tight fork loops

AutoRestart Yes

1. Set the user and group to opendkim user

UserID opendkim:opendkim

1. Specify the working socket

Socket inet:8891@localhost

That’s it for OpenDKIM, now we should restart the service

service opendkim restart

Postfix

Now let’s see what we need to do to configure Postfix to use OpenDKIM.

Execute the following command to see the milters configured

cat /etc/postfix/main.cf | grep "milters"
smtpd_milters = , inet:127.0.0.1:12768
non_smtpd_milters = , inet:127.0.0.1:12768

You can see that we have additional milters we need to put, this one is from the process psa-pc-remote, and it’s part of Plesk

Open /etc/postfix/main.cf with your favorite editor, and add the following to the end of the file

# OpenDKIM
milter_default_action = accept
milter_protocol = 6
smtpd_milters = , inet:127.0.0.1:8891, inet:127.0.0.1:12768
non_smtpd_milters = $smtpd_milters

As you can see we added the OpenDKIM milter too, and milter_protocol is set to 6, this is important, if it’s not set to 6, the psa-pc-remote process will segfault like so,

psa-pc-remote[18523]: segfault at 0 ip 00007fa5be18c034 sp 00007fa5bccffd30 error 4 in libc-2.13.so[7fa5be123000+180000]

And your messages won’t be signed with DomainKey, only with DKIM

service postfix restart

Testing

There is an easy way to test if everything is correct, create an email account if you haven’t already and send a test mail to the following recepients, and the results are cut down because the text is too big* check-auth@verifier.port25.com

==========================================================
Summary of Results
==========================================================
SPF check: pass
DomainKeys check: pass
DKIM check: pass
Sender-ID check: pass
SpamAssassin check: ham* AAAA3QcKCQwA@appmaildev.com

============================================================
SPF result: Pass
============================================================
Domain: myserverplace.de
IP: 144.76.163.46

SPF Record: myserverplace.de
IN TXT = "v=spf1 +a +mx 144.76.163.46 ?all"

============================================================
DomainKey result: pass
============================================================
Signed by: admin@myserverplace.de

PublicKey: default._domainkey.myserverplace.de
IN TXT = "p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDAruBNqdsSCKBLwMrFNNKH8z0e7zmlAic7iRoJsDDJK3IlnW8j6G/T6a93m+jqYc6R38MBAZbeSv2LQJ0SepJEsr4Iqk41WFXPBKnyXReO1RXPW5/YnRe6dpJMEqsmPpl2TjInY7ve/6VCiVDOHn9RRrdB+x7CGeK2crgqSZVlFwIDAQAB;"

============================================================
DKIM result: pass
============================================================
Signed by: admin@myserverplace.de
Expected Body Hash: frcCV1k9oG9oKj3dpUqdJg1PxRT2RSN/XKdLCPjaYaY=
PublicKey: mail._domainkey.myserverplace.de
IN TXT = "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDMziMcgPTWK0kSUKxrgHHzEiWxNkZ2/M0Ugyr/8H9WtoCsJUM+Bc1C9VwqJ6yjTidecDrX7aL0lFZ9Mylku/wtSiPw6KLxMg2LG2vrMzlPTB2lmJNmg/EOu3KPC8BtAuOhXfwVH/ttQbzdKJKWqiCJn7jhF5oqEKnOCORxOQXKIwIDAQAB;"

Logs

You can check the following locations to see if there are errors* /var/log/mail.err

• /var/log/mail.warn
• /var/log/mail.info
• /var/log/syslog

Note

Make sure you enable testing mode for DKIM if you plan to test, you can also cut down the EXPIRY time so the results propagate faster, so to enable testing mode set the key _domainkey to t=y; o=-

References

How to define what MTA is used in Parallels Plesk Panel and how to switch from Qmail to Postfix and back?

Mailserver Administration

Setting up SPF + DK + DKIM

Postfix in Plesk 11.5 on Debian Wheezy

debian wheezy postfix installation configuration plesk dk DomainKeys dkim DomainKeys Identified Mail

Shows up a detailed process on how to set up SPF + DK + DKIM with Postfix in Plesk 11.5 on Debian Wheezy, step by step, and how to test to make sure everything is working correctly

I leased a dedicated server from Hetzner, and I got the Plesk option, for administration, so I don’t have to bother with administration, but turns out I’m not so lucky, I’ve ran into a lot of issues with using Plesk, so I had to do my own fixes.

So let’s take a look at how we can integrate SPF + DK + DKIM with Postfix in Plesk 11.5 on Debian Wheezy.

First things, first, if you are using QMail switch to Postfix, to install Postfix you can either use the GUI, or you can do it from a console.

Here is how to do it from the console.

/usr/local/psa/admin/sbin/autoinstaller --select-release-current --install-component postfix

SPF

Let’s open the DNS Template, you will see there that, there is an entry for SPF

v=spf1 +a +mx -all

This means the SPF is enabled on our domain.

Let’s modify it a little bit to be better, if you are gonna host multiple domains from your server, then you should probably modify it too.

v=spf1 +a +mx +ip4:<ip.mail> ?all* <ip.mail> - Is the IP of the mail server that is responsible for sending the mails, it is automatically filled in when you apply the zones

"SPF DNS Template"

After you do this modification you should apply it

So now my configuration looks like this:

Now let’s check with dig if the SPF is OK.

dig myserverplace.de TXT @ns1.myserverplace.de

You will see in the Answer section I have the following entry

myserverplace.de. 600 IN TXT "v=spf1 +a +mx +ip4:144.76.163.46 ?all"

So everything is ok.

DomainKeys

"Plesk Panel DK Enabled"

First let’s activate DomainKeys, take a look at the screenshot, and compare my options with yours.

Ok, now that this has been enabled, let’s go and enable for the domain in question, if it was already checked, uncheck it press OK, and then check it again and press OK, this is so it will regenerate the DomainKeys data in the DNS zone, as I’ve had some problems with the data not present in the DNS zone file

"Enable DK Domain"

OK, now let’s see if the correct data is there, usually it takes a long time for DNS to propagate between 24-48h, there is a simple way to test if the data is there, by querying the Nameserver that hosts your DNS zone, in my case I host my own Nameserver

dig _domainkey.myserverplace.de TXT @ns1.myserverplace.de

You will see in the Answer section I have the following entry

_domainkey.myserverplace.de. 600 IN TXT "o=-"

Now let’s see if the DomainKey is there too

dig default._domainkey.myserverplace.de TXT @ns1.myserverplace.de

In the Answer section you should see something like

default._domainkey.myserverplace.de. 600 IN TXT "p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDAruBNqdsSCKBLwMrFNNKH8z0e7zmlAic7iRoJsDDJK3IlnW8j6G/T6a93m+jqYc6R38MBAZbeSv2LQJ0SepJEsr4Iqk41WFXPBKnyXReO1RXPW5/YnRe6dpJMEqsmPpl2TjInY7ve/6VCiVDOHn9RRrdB+x7CGeK2crgqSZVlFwIDAQAB\;"

As you can see everything is in place now for DomainKeys to work, now let’s continue on to DKIM

DKIM (DomainKeys Identified Mail)

As always lets update the system first

aptitude update
aptitude safe-upgrade

Now we need to install the DKIM filter, or as it’s called now OpenDKIM, for full specification take a look at their site.

aptitude install opendkim opendkim-tools

Now we need to create the necessary folders so OpenDKIM can work proplery

mkdir -pv /etc/opendkim/keys
chown -Rv opendkim:opendkim /etc/opendkim
chmod go-rwx /etc/opendkim/*

This will create the directory where we will hold the keys for OpenDKIM, after this step let’s take a look at how the process will look like, so we can create a script to automate this.

mkdir -p /etc/opendkim/keys/myserverplace.de
cd /etc/opendkim/keys/myserverplace.de
opendkim-genkey -d myserverplace.de -s mail
chown -Rv opendkim:opendkim /etc/opendkim/keys/myserverplace.de
chmod -v u=rw,go-rwx *

This easily understandble, what happens here.

Now you have two files /etc/opendkim/keys/myserverplace.de

ls -lah /etc/opendkim/keys/myserverplace.de
total 16K
drwxr-xr-x 2 opendkim opendkim 4.0K Oct 9 18:43 .
drwxr-xr-x 5 opendkim opendkim 4.0K Oct 9 19:39 ..
-rw------- 1 opendkim opendkim 887 Oct 9 18:43 mail.private
-rw------- 1 opendkim opendkim 303 Oct 9 18:43 mail.txt* /etc/opendkim/keys/myserverplace.de/mail.private

contains the RSA PRIVATE KEY* /etc/opendkim/keys/myserverplace.de/mail.txt

Contains the record you need to add to your DNS zone

Next set is to setup the key tables, signing tables, and trusted hosts

First let’s prepare the files

touch /etc/opendkim/KeyTable
touch /etc/opendkim/SigningTable
touch /etc/opendkim/TrustedHosts* /etc/opendkim/TrustedHosts

needs to contain some data before we continue, so add the following information to this file, and adjust accordingly

127.0.0.1
localhost
144.76.163.46
144.76.163.57
ns1.myserverplace.de
ns2.myserverplace.de
myserverplace.deSo let’s see what does what:* /etc/opendkim/KeyTable

KeyID Domain:Selector:PathToPrivateKey* /etc/opendkim/SigningTable

The filter used is programmed to read the table by looking for matched domain* /etc/opendkim/TrustedHosts

It will list the top trusted hosts as you desire

Those three files contain all the necessary information for the signing to work.

So in my case for my domain I do.

echo "myserverplace.de myserverplace.de:mail:/etc/opendkim/keys/myserverplace.de/mail.private" >> /etc/opendkim/KeyTable
echo "*@myserverplace.de myserverplace.de" >> /etc/opendkim/SigningTable
echo "myserverplace.de" >> /etc/opendkim/TrustedHosts
echo "mail.myserverplace.de" >> /etc/opendkim/TrustedHosts

So let’s put all this together in a script so we don’t have to do it all the time

#!/bin/bash
# /opt/generatedkim.sh
die () {
echo >&2 "$@"
exit 1
}

[ "$#" -eq 1 ] || die "1 argument required, $# provided, domain required, ex: ./script example.com"

cwd=`pwd`
opendkim="/etc/opendkim"
location="$opendkim/keys/$1"
[ -d "$location" ] && die "There is already a directory in the folder, delete the folder if you want to create a new one"

mkdir -p "$location"
cd "$location"
opendkim-genkey -d $1 -s mail
chown opendkim:opendkim *
chown opendkim:opendkim "$location"
chmod u=rw,go-rwx *
echo "$1 $1:mail:$location/mail.private" >> "$opendkim/KeyTable"
echo "*@$1 $1" >> "$opendkim/SigningTable"
echo "$1" >> "$opendkim/TrustedHosts"
echo "mail.$1" >> "$opendkim/TrustedHosts"
echo
echo "Put this in the DNS ZONE for domain: $1"
echo
cat "$location/mail.txt"
echo
cd "$cwd"

So if we run the script, we should get output like this, and this is the data we need to put in the DNS zone.

/opt/generatedkim.sh test.de

Put this in the DNS ZONE for domain: test.de

mail._domainkey IN TXT "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDPzE0GmvFwAQsgcFzopy4zMNWUbL6JM5XIyjBy3bUnANI5axeb/Lw/GBjUoSFLEiO80Tt8m3A5YrBKcodRQQURYiW6/YtElhLupHyfcxQhfNLU4z9JUOJKPjcpMZCj0Xv873QgVOl+7U605JdBHSPOx4ybBZwDq68cw9YFYRPmEwIDAQAB" ; ----- DKIM key mail for test.de

Unfortunatly I don’t have time to create a script to do this automatically, you can always insert a record in MySQL database so it’s in the ZONE and you can regenerate the DNS Zone from the command line, and I won’t be having a lot of domains, so I can add this entry manually to a domain I want DKIM enabled

Let’s open the domain and go to DNS Settings, and you can click ** Add Resource **

You popuplate the following data in the inputboxes* Record type

TXT* Domain name

mail._domainkey* TXT Record

"DKIM Add DNS Zone"

In the text record you copy a part of the contents from the file /etc/opendkim/keys/myserverplace.de/mail.txt, it data should start from v=DKIM1; k=rsa; to the end, without the quotes as you can see it’s in quotes.

In the example above for domain test.de you add only the following contents in the input box

v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDPzE0GmvFwAQsgcFzopy4zMNWUbL6JM5XIyjBy3bUnANI5axeb/Lw/GBjUoSFLEiO80Tt8m3A5YrBKcodRQQURYiW6/YtElhLupHyfcxQhfNLU4z9JUOJKPjcpMZCj0Xv873QgVOl+7U605JdBHSPOx4ybBZwDq68cw9YFYRPmEwIDAQAB

Well that’s it for this, now let’s check with dig if the record is there

dig mail._domainkey.myserverplace.de TXT @ns1.myserverplace.de

You will see in the Answer section I have the following entry

mail._domainkey.myserverplace.de. 600 IN TXT "v=DKIM1\; k=rsa\; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDMziMcgPTWK0kSUKxrgHHzEiWxNkZ2/M0Ugyr/8H9WtoCsJUM+Bc1C9VwqJ6yjTidecDrX7aL0lFZ9Mylku/wtSiPw6KLxMg2LG2vrMzlPTB2lmJNmg/EOu3KPC8BtAuOhXfwVH/ttQbzdKJKWqiCJn7jhF5oqEKnOCORxOQXKIwIDAQAB"

Well everything is setup up at least from the DNS side, now we need to configure Postfix to use this data and sign the emails.

You can also use the following URLs to check the validity of your key* dkim-key-checker

• DKIM Core Tool

In the selector fields try with both mail, and default, you shold be getting valid results

OpenDKIM

We need to edit the configuration file to configure DKIM, open /etc/opendkim.conf with your favorite editor and add the following lines to the end of the file

# Enable Logging
Syslog yes
SyslogSuccess yes
LogWhy yes

# User mask
UMask 002

# Always oversign From (sign using actual From and a null From to prevent malicious signatures header fields (From and/or others) between the signer and the verifier)
OversignHeaders From

# Our KeyTable and SigningTable
KeyTable refile:/etc/opendkim/KeyTable
SigningTable refile:/etc/opendkim/SigningTable

# Trusted Hosts
ExternalIgnoreList /etc/opendkim/TrustedHosts
InternalHosts /etc/opendkim/TrustedHosts

# Hashing Algorithm
SignatureAlgorithm rsa-sha256

# Auto restart when the failure occurs. CAUTION: This may cause a tight fork loops
AutoRestart Yes

# Set the user and group to opendkim user
UserID opendkim:opendkim

# Specify the working socket
Socket inet:8891@localhost

That’s it for OpenDKIM, now we should restart the service

service opendkim restart

Postfix

Now let’s see what we need to do to configure Postfix to use OpenDKIM.

Execute the following command to see the milters configured

cat /etc/postfix/main.cf | grep "milters"
smtpd_milters = , inet:127.0.0.1:12768
non_smtpd_milters = , inet:127.0.0.1:12768

You can see that we have additional milters we need to put, this one is from the process psa-pc-remote, and it’s part of Plesk

Open /etc/postfix/main.cf with your favorite editor, and add the following to the end of the file

# OpenDKIM
milter_default_action = accept
milter_protocol = 6
smtpd_milters = , inet:127.0.0.1:8891, inet:127.0.0.1:12768
non_smtpd_milters = $smtpd_milters

As you can see we added the OpenDKIM milter too, and milter_protocol is set to 6, this is important, if it’s not set to 6, the psa-pc-remote process will segfault like so,

psa-pc-remote[18523]: segfault at 0 ip 00007fa5be18c034 sp 00007fa5bccffd30 error 4 in libc-2.13.so[7fa5be123000+180000]

And your messages won’t be signed with DomainKey, only with DKIM

service postfix restart

Testing

There is an easy way to test if everything is correct, create an email account if you haven’t already and send a test mail to the following recepients, and the results are cut down because the text is too big* check-auth@verifier.port25.com

==========================================================
Summary of Results
==========================================================
SPF check: pass
DomainKeys check: pass
DKIM check: pass
Sender-ID check: pass
SpamAssassin check: ham* AAAA3QcKCQwA@appmaildev.com

============================================================
SPF result: Pass
============================================================
Domain: myserverplace.de
IP: 144.76.163.46

SPF Record: myserverplace.de
IN TXT = "v=spf1 +a +mx 144.76.163.46 ?all"

============================================================
DomainKey result: pass
============================================================
Signed by: admin@myserverplace.de

PublicKey: default._domainkey.myserverplace.de
IN TXT = "p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDAruBNqdsSCKBLwMrFNNKH8z0e7zmlAic7iRoJsDDJK3IlnW8j6G/T6a93m+jqYc6R38MBAZbeSv2LQJ0SepJEsr4Iqk41WFXPBKnyXReO1RXPW5/YnRe6dpJMEqsmPpl2TjInY7ve/6VCiVDOHn9RRrdB+x7CGeK2crgqSZVlFwIDAQAB;"

============================================================
DKIM result: pass
============================================================
Signed by: admin@myserverplace.de
Expected Body Hash: frcCV1k9oG9oKj3dpUqdJg1PxRT2RSN/XKdLCPjaYaY=
PublicKey: mail._domainkey.myserverplace.de
IN TXT = "v=DKIM1; k=rsa; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDMziMcgPTWK0kSUKxrgHHzEiWxNkZ2/M0Ugyr/8H9WtoCsJUM+Bc1C9VwqJ6yjTidecDrX7aL0lFZ9Mylku/wtSiPw6KLxMg2LG2vrMzlPTB2lmJNmg/EOu3KPC8BtAuOhXfwVH/ttQbzdKJKWqiCJn7jhF5oqEKnOCORxOQXKIwIDAQAB;"

Logs

You can check the following locations to see if there are errors* /var/log/mail.err

• /var/log/mail.warn
• /var/log/mail.info
• /var/log/syslog

Note

Make sure you enable testing mode for DKIM if you plan to test, you can also cut down the EXPIRY time so the results propagate faster, so to enable testing mode set the key _domainkey to t=y; o=-

References

• How to define what MTA is used in Parallels Plesk Panel and how to switch from Qmail to Postfix and back?http://kb.parallels.com/en/5801

Email Bounces / Address requirements

We require that users provide a valid and properly configured email address for the purposes of being able to contact the user in case of problems and other details surrounding their account.

We thus expect users to provide an email account that they actually read on a regular basis.

A personal/non-role account is prefered.

SixXS does not send any email newsletters, hence there is no need to setup a specific account for this.

The current policy is codified and the validity of an e-mail address is determined as follows: #

It is syntactically correct (ie, it has one @)

1. If it is in a domain whitelist, it is accepted
2. If it is in a domain blacklist, it is rejected
3. The local name (part in front of the @) is less than 64 characters
4. The local part is not a role account¹
5. The domain name (part after the @) is less than 255 characters
6. The local name and domain name is valid (ie does not have two consecutive dots), do not have non ISO characters, and are quoted properly
7. The domain is configured properly (see below)

For the domain, the NS and MX records are looked up and resolved to their A and AAAA records so that we have a list of addresses. The MX records are then checked in the white- and blacklist again (such that we can accept e-mail domains hosted on well-known clusters. For each of the A (IPv4) addresses, we check a number of policy DNSBLs (such as zen.spamhaus.org, dul.dnsbl.sorbs.net, and dialups.mail-abuse.org) with the intent to find home-setups, which we do not accept.

Note:In a study performed by SixXS on 32019 e-mail addresses, we found that 11.2% of all addresses (3608) bounced at least once. Of the valid addresses, 9.49% bounced. Of the addresses that our new policy considers invalid, 16.6% bounced. We understand that our policy comes across as harsh, but we assert that it makes a difference to be strict.

"Information"In general: use your ISP's mail address, or a hosted solution, but don't run a mailserver at home - you may be listed in DNSBLs!

Bouncing Email

We expect that email accounts are reachable. If you are not reachable by email we cannot contact you regarding (mal)function of your tunnel. When we receive a bounce on an email address the account will automatically and directly be set into the disabled state. Connectivity provided to a disabled account will therefor be disabled.

If your e-mail address bounced, and you would like to have your connectivity back, update your handle with a valid email address in the appropriate registry and notify SixXS of the change, we can then reinstate your account.

Messages from your mailhost notifying us that the message we send could not be delivered (for example, greylisting longer than 5hrs) and other automatic replies are also treated as bounces and thus will automatically disable your account.

Common Email Configuration/Setup Mistakes

RFC1912 - Common DNS Operational and Configuration Errors lists a number of common problems, for instance MX DNS records pointing to CNAMEs². Domains that are misconfigured are not accepted.

Make sure that the domain of your email address is RFC compliant and has at least 2 distinctly separate working MX servers or a proven cluster solution. If your DNS contains only one MX record and it has a cluster behind it, direct signups will not be able to detect that, thus contact SixXS in that case. Mail servers on dynamically-assigned IP addresses and/or DSL/cable links are not accepted as they have proven not to be stable enough.

Check your domain using for example using ZoneCheck, IIS.SE DNS Check if it looks okay. If you have weird DNS records or had problems in your DNS setup, note well these could get cached in which case you won't be reachable either.

SPF, DKIM, DMARC and forwarding email

SixXS uses SPF, DKIM and DMARC in strict modes. Thus be very mindful when forwarding email as it can cause email to bounce because the address you are forwarding from is not in our SPF records. Also make sure to not break DKIM signed headers.

Forwarding email breaks SPF verification unless you are able to control the receiving end to ignore SPF checks for forwarded messages.

White- and Blacklists

In an attempt to be transparent on the e-mail verification system, here's the currently configured regular expressions for domains and MX hosts from which we automatically reject any e-mail address:

Blacklist

@users\.(sf|sourceforge)\.net$
@(sf|sourceforge)\.net$
@rediffmail\.com$
(@|\.)moerstaal\.nl$
(@|\.)mail386\.com$
(@|\.)(mailhop\.org|(mydyndns|dyndns)\.(com|org))$
(@|\.)homeip\.net$
(@|\.)afraid\.org$
(@|\.)no-ip\.(com|org)$
(@|\.)wdyn\.de$
(@|\.)ath\.cx$
(@|\.)eu\.org$
(@|\.)hushmail.com$
(@|\.)mailinator\.com$
(@|\.)spamgourmet\.com$
(@|\.)163\.com$
(@|\.)trash-mail\.com$
(@|\.)zoneedit\.com$
(@|\.)xname\.org$
(@|\.)42\.pl$
(@|\.)riseup\.net$
(@|\.)(gmx|web|yandex|rambler|alice|mail|qq|126|o2|)\.[^\.]+$
(@|\.)(protonmail|tuta|tutanota)\.[^\.]+$
(@|\.)(hotmail|live|msn|aol)\.[^\.]+$
(@|\.)(yahoo)\.[^\.]+$

As we do not want to encourage the usage of any provider we do not publish the whitelist. Of course, the white and blacklists are not final, if we notice that a domain is unacceptable even though it passes the above tests we may still consider rejecting the address.

If you have a properly set up ISP account, or another email account like one from work we prefer that you provide and use that. Setting up throwaway accounts will be noticed and such accounts will be rejected or disabled. To note, we specifically reject mailinator kind of accounts as these accounts are definitely not intended for proper email communication.

If you would like to file a petition to be added (or removed) from our white or blacklist, please contact SixXS and provide proper argumentation.

¹ = A role account is an account that is not associated with a particular person, but with an office, position, or task. Those doing the task use the account only to do the task. They have other accounts for other work.

² = Using a CNAME in your domain breaks your email because sendmail (and possibly other SMTP software) will rewrite the domain portion of the destination email address to that of the label in the CNAME. See also CNAME records in mail by D. J. Bernstein. Note that having a CNAME for example.tld is of course impossible unless you get the tld to have the same record. Having an MX point to a CNAME record causes additional DNS lookups, which might cross a threshold, and thus cause your mail to be dropped. Additionally "Mail loops back to me" errors might be caused by this. Also see RFC1034 - DOMAIN NAMES - CONCEPTS AND FACILITIES for more details. In short: Don't use CNAMEs in relation to SMTP.