How do I expand pictures from thumbnail in email messages?

[Wrangler54]

I want to set up an email message that includes thumbnails of pictures. The
intent is to expand the thumbnail to an actual size of the image for viewing
while saving on bytes. Is this feasible?

[Mary Sauer]

I don't see how it will make the email any smaller, you will have to include
both the thumbnail and the full size image.