I forgot about this, this is indeed the address to create Messages (not tasks).
Last thing to check: make sure the email address you send it from is the right one attached to the right domain in your personal settings > From email.
I noticed when this happens: Above I have sketched a screenshot of the project - everything is fine there and the message comes to the asana.
BUT, if there is a dot in the project name (using the site address as the project name) - the email comes back with an error. Here is a screenshot of the project where the error.
This is a known issue, but likely something that won’t be prioritised any time soon since it is rarely arising. The best workaround is to rename your project and remove any unsupported characters like “.”
I’ve pinged the bug open for this issue, and will keep you posted here when it’s prioritised and resolved!