At the moment some users are experiencing issues with Braintosses not arriving in Todoist. After some research we've concluded that some/newer Todoist addresses do not comply with email standards (rfc3696/822). In particular the length of the email address.
This means that we can't process the addresses on our server (which does comply) We have raised the issue with Todoist and we urge users affected by this also to get in contact with Todoist.
We hope to have this solved between in a few weeks. Our apologies.
It looks like it is working again. Todoist has changed the length of Todoist address. Number of characters before @ is reduced. Before the length was more than 65 characters before @ and this is not allowed according to email standards.
Please let us know if it is now working again for you too.