Hello Lester Chan!
This is great plug-in. But all the email backup, that are sending this plug-in mark as phishing. I think the main problem is, this plug-in doesn't use the WordPress blog email system.
If this plug-in can send email via the WordPress with proper authentication, it's better.
For an instance, I use "WP-Mail-SMTP" plug-in to send all them mails though my Google apps email address with proper authentication. But this plug-in doesn't use that email plug-in to send email backup to my personal email account.