If you are using Google for your email hosting and have your site connecting to Googles mail servers then you might need to make some changes such that your website can Authenticate into their SMTP servers to send out emails.
Google Now requires you to use 2-Step Authentication on your email account if you are going to use it with apps. This message is telling you that until you set that up, it will use the default mail servers to send emails out from the website.
https://info.dynamicidx.com/knowledgebase/2/Setting-up-SMTP-for-Administrator-accounts.html
https://www.dynamicidx.com/kb/google-2step-verification
