In addition to the information transmitted by one Internet user to another, the email must contain additional service information. The SMTP server uses this information to deliver the mail, and the client's mail receiving software uses this information to classify the mail. Each email has two parts: the header and the subject. Fields in the header can be divided into two types. One is generated by your email program, and the other is added when the email passes through the SMTP server. Among all the fields added by the SMTP server, the message-Id field is the most important for us. This field is added by the SMTP server that you send. This is a unique ID. You can use this number as the mail number. The following table lists the header fields that can be controlled by the user's email program. This does not mean that all fields are required. In fact, you can ignore the header step and only send the body. Add the minimum required fields to your SMTP server. The purpose of the header field is to send a CC from the sender's address to the recipient's address. Other recipients cannot see the recipient's address. Subject topic comments remarks keywords keyword, the idreferences used to further search for emails in-reply-to reply to the current email are almost the same as those in-reply-to. Encrypted: the encrypted date of the encrypted email sending date
