The Virtual Inbox provides insight on how your mailing may render in different email clients and also how your mailing may be classified by ISPs and spam filters when published. Keep in mind that this tool is a test and does not guarantee your mailing will perform the same way when it is actually published. There are many other factors outside of this test that can affect the outcome of a mailing such as: how your audience is reacting to your message (opens/clicks/deleting/moving/flagging/etc), fluctuating mail server/spam filter rules, your publish IP's reputation (our test IP is used), etc.
Navigate to Mailings > View > select a mailing > Modify > Test tab.
Click Virtual Inbox.
Click Run this test now.
The results populate after 10 to 20 minutes.
You'll see different screenshots of what the mailing looks like in different browsers and devices.
The spam filter test results display whether or not your mailing may pass or fail with major ISPs and spam filters when published.
Passed indicates there were no issues found during the test.
Failed indicates that there is likely a deliverability issue that needs to be addressed. Check things like your DKIM authentication, cover exposed URLs, look for typical spam triggers in the subject line and body, avoid using 3rd party short links, and make sure you have a decent amount of text along with your images, etc.