As per NIST 800-63B:

> To maintain the integrity of the authentication factors, it is essential that it not be possible to leverage an authentication involving one factor to obtain an authenticator of a different factor. For example, a memorized secret must not be usable to obtain a new list of look-up secrets.

And further:

> Methods that do not prove possession of a specific device, such as voice-over-IP (VOIP) or email, SHALL NOT be used for out-of-band authentication.