How to enhance the basic email features?

I have the basic email functionality running without problems but I could use some additional guidance on this topic.

I can change the basic text of the emails but how could I use layouts for my emails (eg. Disclaimer in the footer; Logo/Name on top)? I guess that might be the job for a module but I struggle finding the right one. Additionally I don't have a clue how this would work (where to store the basic layout etc.) but I am pretty sure that this cannot be to complicated as it seems to be a pretty common thing to do.

Any other hints on this topic aside from a module recommendation would also be appreciated (best practices, links to additional information).