NSLOOKUP is a quick and convenient way to verify that your DK/DKIM records are set up properly. The policy for DK/DKIM is a TXT record at this location:
_adsp._domainkey.<domain.com>
For the selector record you have to use:
<selector>._domainkey.<domain.com>
For example, do a NSLOOKUP for TXT at: c3po._domainkey.altn.com
Open the Start menu Select Run... Type cmd [Enter] In the command window, type: NSLOOKUP [Enter] Type: set q=txt [Enter] Type: dcontrol._domainkey.tweenpath.net [Enter]
OpenDKIM is method to digitally sign & verify emails on the mail servers using public & private keys. In other words opendkim implements the DKIM (DomainKeys Identified Mail) standard for signing and verifying email messages on a per-domain basis. DomainKeys are implemented to reduce the chances of outgoing mails to be marked as SPAM.
In this post we will demonstrate how to install & configure DomainKeys with postfix (MTA) on CentOS 7, i am assuming Postfix is already installed with following domain and hostname.
Hostname = mail5.freshdaymall.com Domain = freshdaymall.com
Step:1 Set EPEL Repository using below rpm command
OpenDKIM package is not available in the default yum repositories but available in CentOS 7 EPEL repositories
[root@mail5 ~]# rpm -Uvh https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
Step:2 Install OpenDKIM Package using yum
[root@mail5 ~]# yum install -y opendkim
Step:3 Run below Command to create keys
Execute the below command to create public & private keys under folder “/etc/opendkim/keys” Continue reading “Configure DomainKeys- DKIM (OpenDKIM) with Postfix on CentOS 7” »
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
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: Continue reading “Install and integrate DKIM with OpenDKIM and Postfix on a CentOS 6” »
Sharing some sample record value of the post subject for future reference:
SPF:
domain.gov.bd. IN TXT "v=spf1 a mx ip4:1.2.3.4 ?all"
DKIM:
MDaemon._domainkey.domain.gov.bd. IN TXT "v=DKIM1; p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDIaJcNDjvJ6LJ/zyZCIOuaQiLMSC+FBfky8JMFE7LUGlP4LXwmpaKO3Z67x+PVXgYbbFU9nzLaFOfIXTbsCh6LYLBgQF+PNghbTAchQ59IEMrMRsTPCCg95+gKYRupN0B96Uz7rrXifZL8T+yl9MkpIlAsXXs7e8Vhzwa94NdVjQIDAQAB"
DMARC:
_dmarc.domain.gov.bd. 3600 IN TXT "v=DMARC1; p=quarantine; sp=quarantine; rua=mailto:postmaster@domain.gov.bd; ruf=mailto:postmaster@domain.gov.bd; rf=afrf; pct=100; ri=86400"
DMARC Generator:
https://www.unlocktheinbox.com/dmarcwizard/
Once we installed Zimbra Collaboration, we need to be aware of some additional configurations that will allow us to send emails to other Email systems with an improve Security, such Gmail, Hotmail, Yahoo!, etc. This Wiki article will show the different Email Protection resources that exists, depends of the volume of sent email, will be better to implement only one, or two, or maybe all of them, depends.
SPF
Sender Policy Framework (SPF) is an email validation system, designed to prevent unwanted emails using a spoofing system. To check this common security problem, SPF going to verify the source IP of the email and compare it with a DNS TXT record with a SPF content. 
Where needs to be configured?
SPF needs to be configured in the Public DNS Continue reading “Best Practices on Email Protection: SPF, DKIM and DMARC” »
This is a quick and fairly painless way of setting up DKIM, on a postfix server. DomainKeys Identified Mail (DKIM) is a method for associating a domain name to an email message, thereby allowing a person, role, or organization to claim some responsibility for the message and helps verify that your mail is legitimate. This will help your email not get flagged a spam or fraud, especially if you are doing bulk emailing or important emails.
This tutorial is written for debian, so if using centos the paths to some files may be /etc/mail prefix or similar.
First, install dkim-filters
Debian based
apt-get install dkim-filter
Redhat Based
Enable EPEL
yum install dkim-milter Continue reading “DKIM installation on Debian” »
