Hey there @Christiane!

Welcome to the Community! Hope I can help with your preview emails and current question.

Are you receiving any errors when you attempt to preview? We do have limits on the amount of preview emails you can send per billing cycle.  I would also try searching your inbox for the subject line of the email, it may have ended up in another folder due to inbox filters. If you have any firewalls set-up that could also be blocking a preview email, I would ensure that these are disabled or halted at the time of testing. 

When sending a preview email, you have the ability to send it directly to an email address; This makes it easier for spammers to abuse this feature. In order to protect all of our customers, Klaviyo imposes sending limits on preview emails. If you reach your limit, you will need to wait 24 hours after your limit is reached for it to reset.

If you have reached your email sending limit, you can still preview your emails directly within the template instead. To do so, select Show directly in Klaviyo.

I recommend checking your spam/junk and promotion folders. It’s possible that the preview emails ended up in one of these spots. If you do notice the emails in the spam folder, I recommend checking out our article, why some preview emails go to spam for more information.

Hope this helped!
Alex