Sign ups going to receiver’s Junk mail

Hi there,

I’ve recently added the plugin to a client’s website and it’s working great, BUT when someone signs up, the email is being sent to the client’s Junk mail with the following message:

—–Original Message—–
From: A Quiet Place [[email protected]]
Sent: 15 March 2018 12:09
To: Penny Moon
Subject: A Quiet Place: Easy Sign Up

[This sender failed our fraud detection checks and may not be who they appear to be. Learn about spoofing at https://aka.ms/LearnAboutSpoofing%5D

Mary Smith ( [email protected] ) signed up and been redirected to https://www.aquietplace.co.uk

We have tested it in our office with real names and email addresses and every one has done the same thing. Is there a way to stop this?

Thanks very much.

Helen