If you find it interesting, give it to me. I still have to answer your question.
The sending principle of e-mail is very special, including that the sender can modify it himself. This is called mail forgery, and the sending time is also included in the message sent. That is to say, when A sends an e-mail to B, B will not automatically determine the sending time of A from the time of receiving the letter, but A must actively "inform". Therefore, if Party A is not a regular e-mail client, it may provide the function of forging the time or even forging the sender.
As for the specific software, I won't provide it. You give me your email address, and I will send you a letter at 2 100, and you will understand.