There are a few things you can look at here to determine what's going on. A 550 error can mean that the email was blocked by the recipient's email hosting server, and returned to you. If you have a bounce error that you can provide to GoDaddy support, you can submit it here. You can also contact our customer support at one of the numbers below and they can review for you.
If you are consistently hitting the maximum relays on an email address, you may want to look into purchasing additional relays for that address. If you are receiving bounce errors from emails you did not send (but are using up your relays) you may have been spoofed.