I also prefer using HTML when I can. It just gives you so much more flexibility to format things nicely, highlight key points, and generally make your message stand out. A clean layout and a bit of visual flair can definitely make a difference in grabbing attention.
some viral mailers only allow plain text, so I try to make the most of that too. I’ll use eye-catching subject lines, creative symbols (like ★, →, ✔), and line spacing to give the text some structure. Even without HTML, you can still make your emails pop a bit with a smart layout and strong wording.