There are a few types of warnings you might see from Google when using BoldTrail. 

First and foremost, you are going to want to sync your BoldTrail account to your email so that the consumers don't see any potential warnings.

For information on how to sync you BoldTrail account to your email, please following the instructions in this article from BoldTrail: here

Secondly, if you send an email to yourself while using a third party system you will almost ALWAYS see a warning. No one else sees it but you, because Google is trying to protect you when it sees an odd email come from yourself that you didn't send through GMail.