Jeffrey, thank you for your reply. As I stated in my previous post, I not only also checked the spam folder, but also did a global search of my entire mailbox on the text of the subject line in case it ended up in some other odd folder due to some rule I had forgotten about, with no luck either way. The sending id (the email address registered with FAA) is a Yahoo account, and the two test recipients are a gmail account and a mailbox associated with a domain name that I personally own through the MyDomain registrar. I also, on my third try, removed the word "test" from the subject line of the email, thinking that that might be causing the problem. (Though I would have thought it more likely that that might send it to the spam folder, rather than cause it to disappear entirely.)
However, in another thread here containing a similar discussion, someone else said that their missing emails showed up after 3 or 4 days, so maybe FAA is just backed up.