I just open a merge request on yunohost repository.
I really think the issue is best described by @jarod5001 and is due to the fact the check endpoint of senderscore is now behind a fair-use paywall we explode with the yunohost checking process.
As yunohost already check its status through several other services, removing one does not seems to be a problem for me.
Said otherwise: the email we are receiving is NOT about our own server being actually blocked or something. The email just warn us that we are blocked to check whether we are blocked or not ^^