Using If Statement to insert message based on recipient's email domain

I am trying to display a custom message to recipients with a gmail address:

{% if 'gmail' in email %}
As you are a Gmail user, be sure to click "View entire message" at the bottom so you can read the whole email
{% endif %}

I added a debug line that stated:

Debug: Your email is {{ email|default:'' }}

But when I open up  the test message in gmail, the email it prints out is my klaviyo login email (which is not gmail).  

So am I doing this wrong, or is this happening because I am doing it using the Test email functionality?