You should be able to use it with Multi-site without setting up for evey site itself by editing your wp-config.php:
/* Set SMTP settings */
define(‘WPMS_ON’, true);
define(‘WPMS_MAIL_FROM’, ‘[email protected]’);
define(‘WPMS_MAIL_FROM_NAME’, ‘Just a random from name’);
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’, ‘smtp.office365.com’); // The SMTP mail host
define(‘WPMS_SMTP_PORT’, ‘587’); // 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’, ‘[email protected]’); // SMTP authentication username, only used if WPMS_SMTP_AUTH is true
define(‘WPMS_SMTP_PASS’, ‘password’); // SMTP authentication password, only used if WPMS_SMTP_AUTH is true
