HTML emails using Swift "quoted" in Gmail

I am sending a very simple HTML email (it's mainly just a happy holidays image, centered) from my site using Swift.

It works perfectly in several clients (Thunderbird, Outlook Express, Yahoo Mail), but for some reason Gmail considers it as 'quoted con开发者_Python百科tent' and therefore the user does not see any of it unless they click the tiny '- Show quoted content -' link in the email.

This obviously does not work.

What am I doing wrong?

Is the message with the image inside of a conversation? Often, when I send multiple test messages to my gmail account, it will show them as quoted in the conversation stack. Try sending it to a different gmail account and see if it happens again.