Step 1: Open Mac Mail client.
Step 2: Click Mail > Preferences > Accounts.
Step 3: Near the bottom of the window, look for "Outgoing Mail Server (SMTP)", click the drop down arrow and select "Edit SMTP Server List..."
Step 4: Click the "Advanced" button in the middle of the window and make sure Authentication is set to "Password".
Step 5: Click "OK" to close the edit window.