Maybe try changing the URL to this:

“https://mail.google.com/mail/?view=cm&fs=1&tf=1&to={{{Email}}}&bcc=emailtosalesforce…;

I’m also not sure if you can use this syntax with $Model variables:

{{#$Model.EmailtoSF.data.length}}
{{$Model.EmailtoSF.data.0.EmailDomainName}}
{{/$Model.EmailtoSF.data.length}}

Maybe try and see if it works without the data check like this:

”https://mail.google.com/mail/?view=cm&fs=1&tf=1&to={{{Email}}}&bcc=emailtosalesforce…;

A few things. 

I"m not sure what the first merge field is doing:  {{$PropertyOwner.Email.data}}  
And then in the BCC email code you have this:   {{#$Model.EmailtoSF.data}}{{$Model.EmailtoSF.data.0.EmailDomainName}}{{/$Model.EmailtoSF.data}}  I believe it should just be {{#$Model.EmailtoSF.data}}{{EmailDomainName}}{{/$Model.EmailtoSF.data}}

Finally - make sure you have the correct models in your page. 

Follow this tutorial: http://help.skuidify.com/m/supercharge-your-ui/l/102526-including-gmail-to-salesforce-functionality-…

Thanks guys. I’ve got it working. 

Glad to hear you got it working.  Its pretty slick!