Enable MFA with a one-time password. MFA stands for multi-factor authentication, which is a method of verifying a user's identity by requiring two or more forms of authentication. A one-time password (OTP) is a code that is generated randomly and valid only for a short period of time. By enabling MFA with OTP, the administrator can make access to the SaaS email more secure without changing the password policy, as users will need to provide both their password and an OTP to sign in.