With the end of support for our legacy Sync product over the weekend, a number of former users have been in touch wondering what they need to do to their email settings to ensure they don't get undeliverable/bounce-back emails.
The short answer is that you need to remove the Forwarding rules you put in place to send a copy of your emails across to your Sync account.
For more detailed instructions, check out the advice on how to set these forwarding rules up, and basically do the reverse.
Unfortunately, because these settings are contained within your account with these various services, there's no way for us to make the changes for you.