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WP SMTP Mail Settings for Multisite in wp-config GOOD
define('WPMS_ON', true);
define('WPMS_MAIL_FROM', '');
define('WPMS_MAIL_FROM_NAME', 'My WordPress Multisite');
define('WPMS_MAILER', 'smtp'); // Possible values 'smtp', 'mail', or 'sendmail' 
define('WPMS_SET_RETURN_PATH', 'false'); // Sets $phpmailer->Sender if true
define('WPMS_SMTP_HOST', ''); // The SMTP mail host
define('WPMS_SMTP_PORT', 587); // 465 ssl // 587 tls The SMTP server port number
define('WPMS_SSL', 'tls'); // Possible values '', 'ssl', 'tls' - note TLS is not STARTTLS
define('WPMS_SMTP_AUTH', true); // True turns on SMTP authentication, false turns it off
define('WPMS_SMTP_USER', ''); // SMTP authentication username, only used if WPMS_SMTP_AUTH is true
define('WPMS_SMTP_PASS', 'ThePasswordGenius'); // SMTP authentication password, only used if WPMS_SMTP_AUTH is true
Please open the file wp-content/plugins/wp-mail-smtp/wp_mail_smtp.php – at the top of the file there will be the list of all constants that you can use, with descriptions.