How can email headers be manipulated in SMTP?

The correct choice involves manual entry or using programming languages to format headers. Email headers are critical components that convey essential information about the message, such as the sender, recipient, date, subject, and various routing details.

Manipulating these headers can allow for customization of the information included, which is often done through programming languages like Python, Perl, or even through direct code in email applications. For example, developers can create email messages where they specify custom headers to add tracking information or to conform to specific protocols.

Additionally, manual entry of headers is also possible when creating emails in various email clients, allowing users to input specific header values directly. This ability to tailor headers is an important aspect of email management, enabling precise control over the information sent with each message.

Other choices suggest automatic processes or altering server settings that do not provide the hands-on manipulation typically required for email headers. Therefore, the emphasis on manual or programming adjustment accurately reflects the ways in which headers can truly be altered.