Does the gateway still work with email@example.com ?
I could only ever get success by forwarding my mymeteor.ie email account to firstname.lastname@example.org but this has stopped working recently.
I know Meteor withdrew their e-mail service earlier this year so perhaps that is why. The old email is still there if you have an account http://mail.mymeteor.ie/mail/main
I find Meteor bounce anything to email@example.com coming from non Meteor email domains.