Preview Emails and Gmail Spam Filters
Gmail adjusts which emails get caught by its spam filters on a user-by-user basis. This means that Gmail is always learning based on your specific email address and how you interact with email.
If you send frequent preview emails to yourself, but don't necessarily open or click these emails, it's possible that your previews will start to go to your spam folder. If you start engaging with these preview emails, and manually prompt Gmail to place them back in your primary inbox, you should see this trend shift.
To check this, however, you can use a service like Litmus to confirm your emails are passing basic spam filter tests.
Preview Email Limits
When you are sending preview emails you can directly add email addresses without having to add these emails to a list. This makes it easier for scammers to take to abuse this feature. In order to protect all our customers from this, we have sending limits on preview emails. If you have reached 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 also preview/test your emails within the template and view it from within the Klaviyo app.
Corporate Spam Filters and Firewalls
Corporate spam filters and firewalls can be pretty strict if you are sending multiple test emails (or many emails in general) to multiple people at your company. If you are seeing this issue and think it might be a firewall issue, check your firewall settings to ensure you're not doing anything to block Klaviyo emails.
Preview Email Content
Make sure that your test content looks as much like your real campaign as possible. If you are using filler words or filler content than sometimes this will trigger the email client’s spam filter.