This is the most secure method to access servers located in remote branch offices because MFA stands for multi-factor authentication, which requires users to provide more than one piece of evidence to prove their identity. An out-of-band solution means that one of the factors is delivered through a separate channel, such as a phone call, a text message, or an email. This adds an extra layer of security and prevents unauthorized access even if a password is compromised. References:
https://docs.microsoft.com/en-us/azure/active-directory/authentication/concept-mfa-howitworks