Yes, you can use an email signing certificate for both personal and business emails. The purpose of an email signing certificate is to authenticate the sender's identity and ensure the integrity of the email's content. It is useful in any situation where you want to ensure that the recipient can verify that the email came from you and that the content of the email has not been tampered with during transmission. This can be important for both personal and business emails, such as when sending sensitive information or conducting transactions. The email signing certificate is tied to your email address and can be used with any email client that supports S/MIME encryption.