On the LibreOffice - PreferencesTools - Options - LibreOffice Writer - Mail Merge Email tab page, click the Server Authentication button to specify the server security settings.
Enables the authentication that is required to send email by SMTP.
Select if your SMTP server requires a user name and password.
Enter the user name for the SMTP server.
Enter the password for the user name.
Select if you are required to first read your email before you can send email. This method is also called "SMTP after POP3".
Enter the server name of your POP 3 or IMAP mail server.
Enter the port on the POP3 or IMAP server.
Specifies that the incoming mail server uses POP 3.
Specifies that the incoming mail server uses IMAP.
Enter the user name for the IMAP server.
Enter the password.