E-Mail HTML-Signature


is there any possibility to get HTML signatures in E-Mails working?
I found that the rich text editor won’t allow storage of plain HTML, okay. But what about pasting the HTML directly into the database?

Background: I’m writing my own small app and I’m able to modify the Mail Account settings linked to my userId. Inside the App I can reach the AccountMapper to set the signature. Unfortunately: when writing E-Mails the signature appears broken, although correctly in the database.
Do I have to escape something?!?