Information
Sending unencrypted email over the internet increases the risk that messages can be intercepted or altered. TLS is designed to protect confidentiality and data integrity by encrypting email messages between servers and thereby reducing the risk of eavesdropping, interception, and alteration. This setting forces Exchange to offer TLS before using basic authentication.
Solution
Open the Exchange Management Shell and enter the following command:
Set-ReceiveConnector -Identity <'IdentityName'> -AuthMechanism 'Tls, BasicAuth, BasicAuthRequireTLS'
Note: The <IdentityName> value must be in quotes.
Example only for the Identity: <ServerName>\Frontend <ServerName>
Repeat the procedure for each receive connector.