Response: Bounced Address? On a once bad (but now working) email address?

Hey Guys (and girls):

N00b here...

I set up a user for automated notifications in Service Desk, and got an NDR due to a typo in the email address.  After resolving the typo and testing the email address, I am still getting Email Dropped errors everytime I try to send a notification (or an invitation email).

Has anyone seen this before?

Is there a blocklist for NDRs somewhere that I am missing?

Thanks,

A. Breeze