Launching email security insights on Cloudflare Radar

During 2021’s Birthday Week, we and gov domains, it is interesting to see that even 2% of the messages from associated domains are classified as malicious.

Classic TLDs with the highest percentage of malicious email in February 2024.

The reasons that some TLDs are responsible for a greater share of malicious and/or spam email vary — some may have loose or non-existent registration requirements, some may be more friendly to so-called “domain tasting”, and some may have particularly low domain registration fees.The malicious and spam summary shares per TLD are available through the Radar API.

Adoption of email authentication methods

SPF, DKIM, and DMARC are three email authentication methods and when used together, they help prevent spammers, phishers, and other unauthorized parties from sending emails on behalf of a domain they do not own.

Sender Policy Framework (SPF) is a way for a domain to list all the servers they send emails from, with SPF records in the DNS listing the IP addresses of all the servers that are allowed to send emails from the domain. Mail servers that receive an email message can check it against the SPF record before passing it on to the recipient’s inbox. DomainKeys Identified Mail (DKIM) enables domain owners to automatically “sign” emails from their domain with a digital “signature” that uses cryptography to mathematically verify that the email came from the domain. Domain-based Message Authentication Reporting and Conformance (DMARC) tells a receiving email server what to do, given the results after checking SPF and DKIM. A domain’s DMARC policy, stored in DMARC records, can be set in a variety of ways, instructing mail servers to quarantine emails that fail SPF or DKIM (or both), to reject such emails, or to deliver them.

These authentication methods have recently taken on increased importance, as both Google and Yahoo! have announced that during the first quarter of 2024, as part of a more aggressive effort to reduce spam, they will require bulk senders to follow best practices that include implementing stronger email authentication using standards like SPF, DKIM, and DMARC. When a given email message is evaluated against these three methods, the potential outcomes are PASS, FAIL, and NONE. The first two are self-explanatory, while NONE means that there was no associated SPF/DKIM/DMARC policy associated with the message’s sending domain.

Reviewing the average shares across February 2024, we find that over 93% of messages passed SPF authentication, while just 2.7% failed. When considering this metric, FAIL is the outcome of greater interest because SPF is easier to spoof than DKIM, and also because failure may be driven by “shadow IT” situations, such as when a company’s Marketing department uses a third party to send email on behalf of the company, but fails to add that third party to the associated SPF records. An average of 88.5% of messages passed DKIM evaluation in February, while just 2.1% failed. For DKIM, the focus should be on PASS, as there are potential non-malicious reasons that a given signature may fail to verify. For DMARC, 86.5% of messages passed authentication, while 4.2% failed, and the combination of PASS and FAIL is the focus, as the presence of an associated policy is of greatest interest for this metric, and whether the message passed or failed less so. For all three methods in this section, NONE indicates the lack of an associated policy. SPF (summary, time series), DKIM (summary, time series), and DMARC (summary, time series) data is available through the Radar API.

Protocol usage

Cloudflare has long evangelized IPv6 adoption, although it has largely been focused on making Web resources available via this not-so-new version of the protocol. However, it’s also important that other Internet services begin to support and use IPv6, and this is an area where our recent research shows that providers may be lacking.

Through analysis of inbound connections from senders’ mail servers to Cloudflare’s email servers, we can gain insight into the distribution of these connections across IPv4 and IPv6. Looking at this distribution for February 2024, we find that 95% of connections were made over IPv4, while only 5% used IPv6. This distribution is in sharp contrast to the share of IPv6 requests for IPv6-capable (dual stacked) Web content, which was 37% for the same time period. The summary and time series data for IPv4/v6 distribution are available through the Radar API.

Cloudflare has also been a long-time advocate for secure connections, launching Universal SSL during 2014’s Birthday Week, to enable secure connections between end users and Cloudflare for all of our customers’ sites (which numbered ~2 million at the time). Over the last 10 years, SSL has completed its evolution to TLS, and although many think of TLS as only being relevant for Web content, possibly due to years of being told to look for the 🔒 padlock in our browser’s address bar, TLS is also used to encrypt client/server connections across other protocols including SMTP (email), FTP (file transfer), and XMPP (messaging).

Similar to the IPv4/v6 analysis discussed above, we can also calculate the share of inbound connections to Cloudflare’s email servers that are using TLS. Messages are encrypted in transit when the connection is made over TLS, while messages sent over unencrypted connections can potentially be read or modified in transit. Fortunately, the vast majority of messages received by Cloudflare’s email servers are made over encrypted connections, with just 6% sent unencrypted during February 2024. The summary and time series data for TLS usage are available through the Radar API.


Although younger Internet users may eschew email in favor of communicating through a variety of messaging apps, email remains an absolutely essential Internet service, relied on by individuals, enterprises, online and offline retailers, governments, and more. However, because email is so ubiquitous, important, and inexpensive, it has also become an attractive threat vector. Cloudflare’s email routing and security services help customers manage and secure their email, and Cloudflare Radar’s new Email Security section can help security researchers, email administrators, and other interested parties understand the latest trends around threats found in malicious email, sources of spam and malicious email, and the adoption of technologies designed to prevent abuse of email.

If you have any questions about this new section, you can contact the Cloudflare Radar team at [email protected] or on social media at @CloudflareRadar (X/Twitter), (Mastodon), and (Bluesky).

Tune in for more news, announcements and thought-provoking discussions! Don’t miss the full Security Week hub page.

Source:: CloudFlare