Tag Archives: DMARC reject

Google’s Recent SMTP Relay Exploit and DMARC Policies

In April, Google began to see an uptick in spoofing attacks that utilized their SMTP Relay system and compromised Google accounts. They have closed the loophole by May, however, at least 30,000 malicious emails were detected in a two-week period. While this is an extremely small chunk of Google’s email traffic, similar exploits can affect other outbound email providers, requiring patches and constant vigilance.

What is the SMTP Relay exploit?

Google has a great reputation as an outbound sender so email coming from their servers is generally accepted. Google allows their customers to leverage that reputation to send bulk or large quantities of email through the SMTP Relay connection. Before the fix, this enabled any Google customer to send email that looked like another Google customer by simply putting their domain in the “From:” field. For example, SmallCompany.com gets hacked by a scammer and begins to send email that looks like GreatBrand.com, a well respected company also hosted at Google.

  • Blacklists – Google rotates sending IP addresses to minimize the affects of blacklists so a blacklist will not generally catch this issue.
  • SPF Authentication – Both SmallCompany.com and GreatBrand.com have Google’s servers in the SPF record, so it passes Authentication. This might be enough to make the inbox.
  • SPF Alignment – The “From:” address says GreatBrand.com. The <ReturnPath> is SmallCompany.com so it fails SPF Alignment.

So, unless the recipients servers are configured to check SPF Alignment, the Spoofing email may make the inbox. Any brand could then be compromised by a hack to another company in the same outbound email provider.

How do you protect your brand from spoofing?

First, you might think to bring all email in-house. This just compounds your risk. Google and other outbound email providers have more security experts and experience than even most large companies can ever hope to bring to bear. A small or medium business should leverage that experience to protect their brand and get their emails delivered.

Second, adopt DMARC and SPF, and DKIM. A properly configured SPF, DKIM and DMARC setup will help prevent spoofing of your brand and give you insight into potential spoofing issues.

Finally, adopt DMARC “Reject” policies. A DMARC “Reject” policy instructs recipient providers to highly scrutinize in-bound email and reject anything that fails SPF Alignment or Authentication. A “reject” policy would immediately fail email that arrived using the recent SMTP Relay exploit.

Why are few companies adopting “Reject” Policies?

If “reject” policies are great, why aren’t companies adopting them immediately? Unfortunately, there is a lot of fear and misunderstanding about “reject” policies. Our Experts receive push-back every day from our clients. Let’s look at a few examples:

“My legitimate email might be rejected”

While it is possible for legitimate email to be rejected, it is far more likely to be accepted if you have a “reject” policy in place. Inbox providers are looking for relevant content from senders with good reputations. By telling setting up DMARC with a “reject” policy you are telling them that you value your reputation. In addition, the “reject” policy is telling them to throw out emails that might harm your reputation.

“I won’t know if a legitimate source comes online”

Maintaining good email delivery means ensuring that all your legitimate email sources are managed actively. Each source should be included in your SPF record to ensure SPF Authentication. While it is possible for a department to bring in a new 3rd party email source without telling you, these vendors will have detailed information about proper SPF configuration as part of their on-boarding process. If it still slips by, then is it really valid email? Could that rogue department be hurting your brand? Regardless, a comprehensive DMARC reporting tool, like MxToolbox Delivery Center, will alert you that a potential Verified Email Source is missing.

“I won’t know if a phishing attack occurs”

The beauty of DMARC is that by publishing a DMARC record with RUA and RUF tags, you are asking for information about the compliance of emails that come “from” your domain. Inbox providers will tell you through an XML email report. Regular reviews of these reports will give you insight into legitimate sources that fail as well as emerging email threats from phishing attacks using your brand. While you can manually parse these XML files, most companies rely on a reporting tool, like MxToolbox Delivery Center, to process and distill these files into actionable insights.

“It seems complicated…”

While it can take some time to verify your outbound email sources, ensure that SPF and DKIM configurations are correct and monitor DMARC reports to ensure that everything is properly tuned, moving to a “reject” policy is not very complicated. MxToolbox Delivery Center uses our experience with DMARC to make recommendations on when to move to a “quarantine” or “reject” policy and how much of your mail to send under that policy.

If you still find it complicated, you can leverage our Expert Managed Services to help you with your configuration.

What do MxToolbox Experts recommend?

Our team of Experts is always evaluating the newest email technologies – DMARC “reject” policies are a necessity to help improve your brand reputation by stopping phishing attacks using your brand. If more brands adopted DMARC “reject” policies, phishing attacks would be greatly reduced. It’s time for all companies to be DMARC compliant – Get Started Today!