An e-mail signature is a type of business card within the world of the internet and it leaves behind a professional impression, especially with business contacts. In it, your partners and customers find important information – such as your telephone number and extension or the internet address of your homepage. Before you can create an e-mail signature, you should know what a professional e-mail signature should contain – there are special guidelines, especially at the business level, that you should observe to make sure your signature is legally valid. How you set up your e-mail signature differs slightly, though, depending on the e-mail provider or program.