Add an option to add multiple / change the signature based on the theme someone is using.
Many company's use signatures in their emails. Most of these signatures have an image and some text. When designing these most people will only check if looks great on white mode. But when you have darkmode on, it doesn't look so good anymore.
The whole concept of signatures in emails should be rethought! Honestly, there is so much clutter in there - you don't need that! Instead I would love to see the signature being a separate part of an email like you have a subject, a body, attachments and for that there should be "accompanying information". It could than be handled as to only show when printing/ archiving or in a "legal mode". At the same time you could still use the old way of working with signatures by means of "stuff to insert and show at the end of each of your mails that aren't purely bloating you emails up without adding to conversations".