Secure access, even in case of mishandling
The link from your encrypted email is useless without the access code. You thus prevent any accidental or malicious opening.
Encryption alone protects content. Authentication guarantees that only the right person accesses it.
An SMS code, a random code sent in a separate email, or Microsoft authentication adds an extra verification layer that prevents any unauthorized person from opening the content.
These authentication methods greatly reduce the risks associated with human error, hacking, or unintentional transfers.