How Does an Email Server Work?

Ever wonder how does an email server work? Email is an integral part of daily life, but most people take the processes behind email for granted. Email wouldn't be possible without email servers.

The history of email servers.
Email didn't originate with the Internet. Email was actually around before the Internet ever existed. It was developed as part of the government defense network known as ARPANET. The first modern email was sent via ARPANET in 1971, before the Internet ever saw the light of day. Today's email servers are different beasts, though.

Servers and clients.
An email server is just another system of servers and clients. An email server is actually an email server program that runs on a computer specially optimized to handle email requests. Clients are the computers that connect to the server and make requests from it, and clients may also refer to the program or protocol by which the computer connects to the server. An email client is another name for an email program that communicates directly with the email server program to retrieve your mail.

A hosted email server can refer to a few different things. In one context, a hosted email server is another term for an email server where you can buy a specific domain name for your emails. You can get a Web host, for example, that also hosts email, and then you can run an email server program on the server, like Microsoft Exchange Server. Since Microsoft Exchange Server is extremely expensive, small businesses may want to use a hosted email server for Microsoft Exchange, saving the costs of buying the software and hardware to develop the infrastructure.

SMTP.
SMTP is one type of email server program. SMTP is short for Simple Mail Transfer Protocol. SMTP is an outgoing mail server. SMTP protocols work only for sending mail; you can't receive mail using SMTP.

If the SMTP server is communicating within its own network-for example, if you're sending a Gmail message to another Gmail user-the SMTP server simply sends the file over to the incoming mail server.

If you're sending an email to a server outside of your system, such as from Gmail to Hotmail, the SMTP server has to ask the Domain Name Server, or DNS server, for the IP address to connect to the correct server. From there, the message goes to the system's SMTP server, which then forwards it to the incoming mail server and on to its recipient.

POP3 or IMAP.
POP3 and IMAP are incoming email protocols. POP is short for Post Office Protocol, and POP3 is one of the most common types of incoming email protocols. With a POP3 incoming mail server, when you download that mail onto your local computer, it's automatically removed from the server. The only copy then exists on your local computer, and if you need to access it elsewhere, you're out of luck.

IMAP is a newer incoming email protocol, and it functions differently from the POP3. IMAP emails stay on the server unless you specifically tell the server to delete them, so you can access the emails from anywhere and download them to multiple locations, if you have the need.