Email Authentication through SPF, DKIM and DMARC

Sender Policy Framework (SPF), DomainKeys Identified Mail (DKIM) and Domain-based Message Authentication, Reporting and Conformance (DMARC) are email authentication methods to prevent email spoofing.  One or more methods are also increasingly required by major mail hosts to prevent spoofing.  And lacking the proper authentication requirements can result in mail rejections.

A SPF is defined by adding a TXT record to the domain's DNS.  The SPF for sending mail through Discountasp is:

v=spf1 include:internetmailserver.net -all

If hosting DNS through Discountasp, the SPF record would be added through the DNS Manager:  Discountasp Control Panel > DNS Manager > I Understand and Agree > Primary Domain > TXT Record Manager > New

Domain Name: Field is left blank

TXT Data: v=spf1 include:internetmailserver.net -all

TTL: 3600

Like with other DNS record updates, it will take some time for propagation to complete.  To monitor DNS propagation https://www.whatsmydns.net/ may be used. 

To test the SPF record, see the Testing SPF, DKIM and DMARC section below.

DKIM is a combination of a SmarterMail setting and TXT record.

First log into the SmarterMail web interface as the domain administrator (default is postmaster).  If the web interface address or password isn't known, log in automatically at:  Discountasp Control Panel >  SmarterMail Manager > SmarterMail Management Login as Primary Admin

After clicking Enable, a pop-up with a TXT record will be displayed.  Add the TXT record to the domain's DNS and click Save.  SmarterMail will then automatically perform a DNS check to enable DKIM.

Domain Name: The "Text Record Name"

TXT Data: The "Text Record Value"

TTL: 3600

Partly because it involves reporting, please note there are too many permutations to completely cover DMARC in this article.  Though there are many resources available online with detailed information in cases where a specific setup is preferred or required.  When both SPF and DKIM have already been added to a domain, a very basic DMARC record would be

Domain Name: _dmarc

TXT Data: v=DMARC1; p=reject;

TTL: 3600

It is important to be aware that the "p" in the record is the policy and is set to reject messages that don't pass SPF and DKIM requirements.  Making it imperative that the record be added after SPF and DKIM and not be used on a pointer domain where DKIM may not be set.

For reporting, three additional values can be added to the record

rua: DMARC Aggregate Feedback Reports

ruf: DMARC Failure Reports (where supported)

fo: Failure Reporting Options (1 = generate DMARC failure report for SPF or DKIM failures)

Example data

v=DMARC1; p=reject; rua=mailto:[email protected]; ruf=mailto:[email protected]; fo=1

Because the report addresses are public and discoverable, it would be advisable to create a new separate email address to receive the reports.

A simple test of SPF, DKIM and DMARC can be performed by sending an email to a Gmail recipient and checking the email header.  After the email is received, view it, click the three vertical dots for more options then Show Original.

If set up properly, there should now be three PASS notifications on the Original Message page.