Hi Amy14,
That definitely sounds like a bit of a hassle, especially when everything's been working fine before. What's likely happened here is that the recipient's email address has ended up blacklisted on our end, which can cause those "diagnostic code: rejected" bounce-backs. The reason you've seen others have this fixed via private message is because we need to grab a few account details to whitelist the affected email address and that can't be shared publicly for privacy reasons. To get this sorted nice and quick, the best move is to jump onto our live chat support through our virtual assistant, MOCA, or submit a case via My Account. They'll help get things whitelisted and your invoices flying out again in no time.
Regards,
Sai
