I just tested sending an e-mail to firstname.lastname@example.org using 2 different e-mail accounts, and they worked. However, it's possible that the e-mails you're sending are accidentally being blocked as spam. I've had that happen on my regular business e-mail account, email@example.com. E-mails that should get delivered get put in the spam folder by the e-mail server software.
If you could, send me an e-mail at firstname.lastname@example.org with the same e-mail account you used to send the e-mail to email@example.com. That way, I'll be able to see if your e-mail is accidentally being blocked as spam on the tiftmerritt.net e-mail server.
Also, make sure you're using tiftmerritt.net rather than tiftmerritt.com.