Hidden preheader text: you should not see this in the message body.
HTML and image support test
1. Inline <svg> (green = yes)
2. SVG imageSVG not shown
3. WebP imageWebP not shown
4. AVIF imageAVIF not shown
5. PNG image (control)PNG not shown
6. GIF image (displays)GIF not shown
7. data: URI image (green = yes)
8. <video> (fallback text = no)
9. Emoji😀 ✅ 🎉
10. <details> (hidden text = yes)
Open meHidden details text
11. Outlook-only block (mso)
Non-Outlook content
12. Hidden preheaderPass if the sentence about hidden preheader text does not appear above the heading.
13. background attribute 
14. <button> element
End of test. MailSlurp email client support report, v1.