It’s a shame that you decided to rate this plugin with 2 stars because of this issue, because the phishing warning from Gmail (and other email clients) has absolutely nothing to do with this plugin. That is due to Gmail finding fault with your server and the way that mails are sent from your WordPress installation. This plugin uses the standard wp_mail() function as well as the default ‘from’ name and address that your WordPress installation supplies, so if you are getting phishing warnings then you have a larger problem that has absolutely nothing to do with this plugin.
In the future, don’t be so quick to blame a tool that isn’t at fault ??
