Once you've added an email account in Mail for Windows 10, you can start sending emails. You can add a custom signature to every email message.
Add a signature to email messages
Mail for Windows 10 comes with a default signature: Sent from Mail for Windows 10. If you have multiple accounts, you can create a text-based signature for each account.
Choose Settings > Signature.
Choose an account or check the Apply to all accounts box.
Ensure the Use an email signature slider is set to On, and enter your signature. You can enter multiple lines of text. Your signature is saved automatically.
You can't create hyperlinks, change the font or font color of your signature, or add images.
A signature is either on or off for a specific account. If you turn a signature off for one or all accounts, you can't add the signature manually while creating a new message.