What part of an email can be considered optional in the sender's information?

The signature in an email is indeed considered optional in the sender's information. While many people include a signature as a form of professional courtesy or branding, it is not strictly necessary for an email to be sent or received. A sender can choose to leave the signature out, and the email would still fulfill its purpose of communicating a message.

On the other hand, the subject line, body text, and recipient address carry essential roles in the structure and function of an email. The subject line helps the recipient understand the topic of the email at a glance, the body text contains the actual message, and the recipient address is critical for directing the email to the correct individual or group. Without these components, an email would not be effective in delivering information.