It looks like Microsoft are getting pickier about email address syntax, rejecting mail that uses illegal address formats. That might be what’s causing that “550 5.6.0 CAT.InvalidContent.Exception: DataSourceOperationException, proxyAddress: prefix not supported – ; cannot handle content of message” rejection. Why do we care? It’s good to send syntactically valid...
Right at the end of January, Microsoft appears to have made couple of changes to how they’re handling authentication. The interesting piece of this is that, in both cases, Microsoft is taking authentication protocols and using them in ways that are slightly outside the spec, but are logical extensions of the spec. The first is an extension of DMARC. They’re rolling out inbox flags for...
At the end of last year, Steve wrote a post about the different types of authentication. I thought I’d build on that and write about the costs associated with each type. While I know a lot of my readers are actually on the sending side, I’m also going to talk about the costs associated with the receiving side and a little bit about the costs for intermediaries such as CRM systems or...
Multiple times over the last few weeks folks have posted a screenshot of Google Postmaster tools showing some percentage of mail failing DMARC. They then ask why DMARC is failing. Thanks to how DMARC was designed, they don’t need to ask anyone this, they have all the data they need to work this out themselves. The DMARC protocol contains a way to request reports when DMARC authentication...
A few ISPs use the d= value in the DKIM signature as a way to provide FBL and reputation data to senders. This has some good bits, in that senders can get FBLs and other information regardless of the IP address they’re using and whether or not they have sole access to it. There are also some challenges with using the d= as a data identifier. One of them is that ESPs may not be able to get a...
I just got some mail claiming to be from “Bank of America <secure@bofasecure.com>”. It passes SPF: Received-SPF: Pass (sender SPF authorized) identity=mailfrom; client-ip=185.235.176.160; helo=bofasecure.com; It passes DKIM: Authentication-Results: mx.wordtothewise.com (amavisd-new);Â dkim=pass (1024-bit key) header.d=bofasecure.com The visible RFC 822 From address is strictly...
A security researcher has identified a rendering flaw that allows for “perfect” phishing emails. From his website: Mailsploit is a collection of bugs in email clients that allow effective sender spoofing and code injection attacks. The spoofing is not detected by Mail Transfer Agents (MTA) aka email servers, therefore circumventing spoofing protection mechanisms such as DMARC...
The US National Cybersecurity Assessments & Technical Services Team have issued a mandate on web and email security, including TLS+HSTS for web servers, and STARTTLS+SPF+DKIM+DMARC for email. It’s … pretty decent for a brief, public requirements doc. It’s compatible with a prudent rollout of email authentication. Set up a centralized reporting repository for DMARC failure...
It’s easy to tell if a domain is using SPF – look up the TXT record for the domain and see if any of them begin with “v=spf1”. If one does, they’re using SPF. If none do, they’re not. (If more than one does? They’re publishing invalid SPF.) AOL are publishing SPF. Geocities aren’t. For DKIM it’s harder, as a DKIM key isn’t published at a...
We know that legitimate email sent with valid SPF and a DKIM signature often breaks in transit. SPF will fail any time mail is forwarded – via a mailing list, a forwarding service used by the recipient, or just ad-hoc forwarding. DKIM will fail any time the message is modified in transit. That can be obviously visible changes, such as a mailing list tagging a subject header or adding a...
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