SMTP

SMTP is an acronym for Simple Mail Transfer Protocol.

“SMTP specifies that a computer sending an e-mail must contain information identifying the sender, generally referred to as ‘hello domain’ information, as well as certain recipient information. The hello domain, in turn, contains the internet protocol (‘IP’) address and domain name of the sending party. IP addresses are unique strings of numbers; each computer accessing the Internet is generally assigned one. For convenience and efficiency, IP addresses of many computers are given textual equivalents known as ‘domain names.’. . . Additional contact information is provided as well. . ..

“When e-mail is sent, the hello domain and sender information exist as part of the transmission information of the e-mail. E-mail servers and routers starting with the sender’s Internet Service Provider (‘ISP’) relay the message forward until it reaches the e-mail servers of the recipient’s ISP, which then direct the e-mail to the intended recipient. These server interactions include the presentation of the sending e-mail’s hello domain. Essentially, the sending computer identifies itself and presents the hello domain of the e-mail.

"Each time the message passes through a different server, a record of that transaction is added to the routing information. Thus, using the e-mail’s routing information, one can retrace the exact servers it went through to reach its destination, as if each post office or mail sorting facility added its own postmark to a letter. Furthermore, a server along this chain could choose to block the message from going further. The sender, however, has no way to control or predict the pathway his message will take to arrive at its destination. In fact, the message can be broken up and sent in pieces through multiple unique pathways. Despite this inherent unpredictability, the last server through which the message passes before reaching the recipient is his ISP’s server. . . .”