You could use a website my agency uses called Email On Acid. This allows you to see email previews in multiple formats i.e. Yahoo, Gmail, Outlook, Apple. You can also view them in mobile versions.

Hey @wouter 

Thank you so much for coming to the Klaviyo Community for help with your preview emails!

There are a few reason gmail is not receiving your preview emails. First, is this a new Klaviyo account you are sending from? Some email host require a warming period before they start allowing your message to be delivered. Also, have you added the Sending Domain: send.klaviyo.com From Address: Your Send-from email to your email host settings to accept emails from this new sending domain? Sometime gmail is strict with what they will allow in your inbox and by added this as a “safe” sender will allow the preview emails to be delivered. Lastly, how many test emails have you sent? Klaviyo only allows a certain amount of preview emails to be sent in order to protect your deliverability.

@BryanzaleLP suggestion does work but you should be able to accomplish all of this within the Klaviyo platform without using a third party. 

Thank you both for being part of the Klaviyo Community. I look forward to your responses or any solutions you may have found as you explore the Klaviyo Community and our other resources like the Help Center!

@stephen.trumble Thanks for the info! I did not know that.

Thanks @stephen.trumble & @BryanzaleLP for your suggestions. 
I did add, send.klaviyo.com to my Gmail contacts. So far this didn’t help. I’m not receiving any of the preview mails. I do receive other Klaviyo mails btw.
My account is active since 5 or 6 weeks and I have been sending roughly 10 preview emails.

Tnx