As an alternate solution until CCP implements evemail drafts:
If I understand the function correctly notes are saved while you type thus if you type your evemail in your in-game notepad they should save serverside and once done you can copy past (even with formatting) to your evemail. Though haven’t tested this but as far as I know notes are saved as you type them but if not you can close and reopen them every now and then which should save them regardless of an auto-save feature.