I finally tracked down the problem that caused some, but not all, mailers to fail to send mail to jokeefe at jamesokeefe dot org.
I had setup a CNAME record for jamesokeefe.org that pointed to jokeefe.typepad.com. This setting resulted in some servers getting the typepad domain name server and not the correct domain name server.
Those servers that got the typepad dns would email to firstname.lastname@example.org. Removing this CNAME record and instead setting up an A record that pointed jamesokeefe.org to www.jamesokeefe.org appears to have fixed the problem.
Various folks who have had problems in the past, are now able to email jokeefe at jamesokeefe dot org. I am most pleased, though it took me too long to fix it.