Generally speaking, TLS Encryption for email refers only to the encryption of the transport between two sites. The sites must both support it and the default for both mail servers must be to use it, unless both sides are specifically set to use it when talking with each other. However this has nothing at all to do with the storage of the email.
Generally speaking, there is no safe way to send HIPAA data in the body of an email. The only way to do it would be to encrypt the data ahead of time, attach the encrypted file to the email, then have the recipient decrypt it.
TLS is not an encryption standard for at-rest data like AES would be. TLS is only transport-level encryption.
So when is TLS encryption HIPAA-compliant? When it is level 1.2 or greater and only for the duration of transport from site to site. Not before and not after.
Another example is looking at a web page. If it is an HTTPS link then chances the data was sent from the server to you using TLS 1.2 or greater. It does not mean the the data was encrypted on the server, and it certainly does not mean that it is encrypted in your browser because you are looking at it.