1. Copy the source code from your emails in the tool you use to create emails in HTML (e.g. Marketo's Email Editor)
2. Click the Source button in your template editor.
3. Paste the source code there.
4. Click Save.
If you see the error "Error - to remove the style/java/html tags," it means you have some styling we don't support. You should search the Source code for the word style and delete everything from <style> through </style>.