DMARC

DMARC (Domain-based Message Authentication, Reporting and Conformance) is a standard that allows you to set policies on who can send email for your domain based on DKIM and SPF. If you are new to email authentication, we recommend first reading about SPF and DKIM.

In combination with SPF and DKIM, a DMARC policy in DNS allows you to set rules to reject or quarantine (junk folder) emails from sources you do not know. Through support from ISPs (Gmail, Yahoo, Microsoft and more) DMARC also allows you to receive reports on sending activity for your domain. DMARC is based on a DNS TXT record that is added to the _dmarc subdomain of your domain. The format and values of the record defines your DMARC policies as well as where you would like to receive reports.

Acenet strongly recommends setting up a specific email address for the DMARC feedback reports. You can use either "postmaster@" or possibly "dmarc@" your domain as the mailto address in the DNS record below.

Implementing DMARC on your domain

DMARC is extremely powerful as a tool to stop email spoofing. At the same time, it's highly complicated and risky to implement. If you set a DMARC policy without knowing all of your email sources (mailboxes, email marketing, CRM, transactional email, server alerts, etc) you could potentially reject legitimate emails. It is recommended that you first set your DMARC policy to p=none. This will allow you to receive reports on the sending sources of your emails and slowly align all outgoing email with DKIM and SPF for your domain.

To enable DMARC, add a TXT record to your domain's DNS zone file.

1) Log into cPanel

2) Under Domain, find your domain name and then click the Manage link. It has a wrench near it.

3) Under Add a record, click the down arrow, and select Add DMARC record.

4) In the TTL textbox, enter 14400

5) In the TXT Data box, enter the DMARC configuration DATA.

{{{1}}}

6) Click the optional Paramaters link to display additional settings.

7) Select Quarantine

8) You will need to enter an email address where mail reports will be sent to. Acenet recommends a new box to be used exclusively for mail reports. enter this address under Send Failure Reports to. This can be checked periodically and then emptied.

9) Click the blue Add Record button.

Testing your DMARC DNS record

After adding the DNS TXT record for DMARC, please allow a few hours for DNS Propagation.

Microsoft Windows

Type nslookup at a command prompt. At the nslookup> prompt, type the following commands, replacing example.com with the actual domain name.

<syntaxhighlight lang="bash"> set type=txt _dmarc.example.com </syntaxhighlight>

You should see output that resembles the following

<syntaxhighlight lang="bash"> _dmarc.example.com text =

    "v=DMARC1;p=none;rua=mailto:[email protected]"

</syntaxhighlight>

Linux and MAC OS X

Type the following command at the command prompt. Replace example.com with your own domain name:

<syntaxhighlight lang="bash"> dig +short txt _dmarc.example.com </syntaxhighlight>

You should see output similar to the following.

<syntaxhighlight lang="bash"> "v=DMARC1; p=none; rua=mailto:[email protected]" </syntaxhighlight>