509tyler on "[Plugin: WP Mail SMTP] SUGGESTION - hide SMTP password"

You can set a constant in your wp-config file if you do not want the password stored in the DB like this:

define('WPMS_SMTP_PASS', 'your_password_goes_here'); // SMTP authentication password, only used if WPMS_SMTP_AUTH is true

See this article:
http://www.dangtrinh.com/2015/10/smtp-emailing-for-wordpress-multisite.html