Page 43 - Cyber Defense eMagazine - November 2017

Here are three tips that can help you properly set DMARC policies:

• First, test with a “none” policy. Mailboxes that support DMARC should still send reports
on messages that fail DKIM and SPF checking. This can help you identify legitimate
email sources from your domain that you may have overlooked.

• Make sure you follow the correct syntax when configuring your DMARC DNS record.
Dmarc.org has a wide range of tutorials and guides that can help you with this.

• Once you have finished testing your DMARC record, change the policy to “reject” or
“quarantine” to instruct recipient mailboxes on how to handle spoofed messages from
your domain.

Configuration issues aren’t the only obstacle here. DMARC also suffers somewhat from the
“chicken or the egg” conundrum. Some companies wonder why they should invest precious
resources into testing and deploying DMARC records for their domain when recipient mail
servers don’t bother verifying emails against them. It is commendable that DMARC’s adoption
rate was 60 percent by mailboxes after just one year, but that percentage has only grown by 10
percent as of 2016 according to a recent report by Return Path. DMARC verification by recipient
servers must increase as well, in order to help slow the growing epidemic of spam and phishing.

It is in everyone’s best interest to fully adopt protocol standards like SPF, DKIM and DMARC.
While they may take some effort to deploy, the benefits are more than worth it. Preventing
spammers from spoofing your company’s domain can help you avoid costly reputation damage
and shield your customers from annoying, potentially malicious emails. Enabling DMARC
verification on your own mailboxes for incoming messages can also drastically reduce your
chances of falling for convincing phishing attacks.

About the Author

Marc Laliberte is an Information Security Threat Analyst at
WatchGuard Technologies. Specializing in networking security
protocols and Internet of Things technologies, Marc’s day-to-
day responsibilities include researching and reporting on the
latest information security threats and trends. He has
discovered, analyzed, responsibly disclosed and reported on
numerous security vulnerabilities in a variety of Internet of
Things devices since joining the WatchGuard team in
2012. With speaking appearances at industry events and
regular contributions to online IT, technology and security
publications, Marc is a thought leader who provides insightful
security guidance to all levels of IT personnel.

43 Cyber Defense eMagazine – November 2017 Edition
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