These changes cause narrowing of the lumbar spinal canal which is known as spinal stenosis. Spinal stenosis is like the lime build-up on the inside of a garden hose. Over time, it narrows the diameter of the hose, just as spinal stenosis narrows the spinal canal.
SMTP Protocol: The SMTP (Simple Mail Transfer Protocol) protocol is used by the Mail Transfer Agent (MTA) to deliver your eMail to the recipient's mail server. The SMTP protocol can only be used to send emails, not to receive them.
Using Port Numbers and Protocols. Simply knowing how to send a message to a computer is not sufficient. Most computers need to access various services across the Internet, and some computers provide those services. There needs to be a way to separate the incoming traffic and direct the information to the appropriate program.