I'm writing a presentation for web designers on HTML email. They understand web design well, but do not realise the differences in designing for Email. The topics I have so far are:

Keeping the design simple because of old tech; The table structure and sticking to the rigid structure (no images spanning more than 1 column etc.); font restrictions; using images for more complex design features, but pressing home the drawbacks of this; making sure they do not spend too much time / effort on emails when it could be better utilised elsewhere websites, apps etc.

Is there anything else important you guys think I have missed?

Thank you!