Hi EvilKermit
Thank you for your post. I'd like to extend you a warm welcome to the Community Forum. I hope you find it a valuable resource.
Once you send an email to your client MYOB will notify you that it was being sent and delivered. However, on your customer's end they are not receiving your email and you've tried to send to your own email and it goes through.
If this is the case, it is possible that the receiver has blocked the domain (app.myob.com) or marked it as a spam. Make sure that the receiver will whitelist the domain, and marks as safe and not spam.
Please feel free to post again I'm happy to assist.
If my response has answered your enquiry please click "Accept as Solution" to assist other users find this information.
Cheers,
Princess