Broken SPF…what does it mean?

People sometimes write in and ask "what is the impact of a broken SPF record"? The net effect of a broken SPF record is that receivers can't reliably use SPF to determine the legitimacy of the domain's email.  *Some* receivers might ignore the broken parts of an SPF record and keep checking, but out of the box all SPF implementations will barf, and you'll be left with a record that is introducing uncertainty into email performance. We've discovered an odd…
dmarcian
10 October 2015

PTR mechanisms in SPF records

If PTR mechanisms are detected, the current diagnostic output is: Warning: PTR mechanisms SHOULD NOT be used and cannot be resolved using this diagnostic tool.  More info at <this page!>. What does the PTR mechanism mean?  When an email receiver gets a piece of email and the PTR mechanism is in the sender's SPF record, the receiver will look at the incoming IP address and do a "PTR" lookup.  For example, if the sender is sending email from IP address…
dmarcian
9 October 2015

Brief history of email authentication

Email is huge (largest deployed application on the Internet?) and it takes a long time to change the fundamentals. 2003: First SPF draft 2004: First DomainKeys draft (predecessor to DKIM) 2006: First DKIM draft PayPal begins work with Yahoo on authentication-based model 2007: BITS Email Security Working Group publishes paper recommending TLS + SPF + DKIM for email DKIM RFC published PayPal + Yahoo blocking based on DomainKeys+SPF goes live 2008: PayPal publishes "A Practical Approach To Managing Phishing" 2009:…
dmarcian
5 October 2015

ADSP and DMARC

A dmarcian.com user once asked: I can't seem to find the answer to this question anywhere on the Internet (it may just be me not fully understanding the standards), so I thought I'd ask you. If I have DMARC set up in my DNS (which I do) and also ADSP (also do), which one takes precedence? I'm also assuming that I am in overkill mode and that DMARC is enough. Your input would be appreciated when you have a moment.…
dmarcian
4 October 2015
Deployment

What is the difference between SPF ~all and -all?

SPF is all about publishing a list of servers that are authorized to send on behalf of a domain. After writing out a list of servers in the form of an SPF record, the right thing to do is to end an SPF record with something that says "and everything else on the Internet is NOT authorized". The way the above is written is to use the "all" mechanism.  This mechanism matches everything.  By adding a prefix of "~" or…
dmarcian
3 October 2015