A mail server is a computer that handles email messages using standardized protocols. Email clients communicate with servers to send and receive messages, which are split into data packets and reassembled at the receiving end. Spam filters block certain IP addresses, and mailing lists use different software to identify legitimate traffic. Some people try to install mail servers on their computers, but this is often a breach of contract. Commercial mail servers also use virus filters and trojans.
A mail server is a computer that acts as an electronic post office for e-mail. Mail exchanged across networks is passed between servers running specially designed software built around agreed standardized protocols for handling mail messages, the graphics they may contain, and attached files. All Internet Service Providers (ISPs) have mail servers for handling their customers’ mail messages, sometimes referred to as private mail servers. Some websites also offer public email services, using their own servers.
An email client or email program allows a user to send and receive email by communicating with mail servers. There are many types of email clients with different functionality, but they handle all email messages and servers in the same basic way.
When an e-mail message is sent, the e-mail program contacts the author’s ISP’s mail server to pass the message to it. The server is normally named mail.(isp).com, although it might be named after the Send Mail Transfer Protocol, smtp.(isp).com. Examine the message’s embedded headers for addressing information. These headers are usually not visible in an email client unless the user configures the program to show the headers, but critical information is contained here.
The email is sent along with the address, which may involve going through several routers. The message is actually split into discrete data packets and reassembled at the receiving end. Routers are computers that receive network data and reroute it via the shortest possible path. Assuming nothing goes wrong, the email will reach its destination within seconds or minutes of being sent.
Once the receiving mail server has the message, it stores it in a virtual mailbox. The mail will stay here until the recipient uses their email client to check for new mail. When it does, the mail program contacts the receiving server, sometimes called a POP3 mail server (for Post Office Protocol 3) as in pop3.(isp).com, or simply mail.(isp).com. When your e-mail program requests mail, it checks for any messages addressed to that user. If found, the server transfers messages to the client as requested. Those found on public websites work the same way as ISP mail servers.
Due to the large amount of junk mail called spam, some mail servers are configured to block certain sets of IP addresses from which spam has been received. An Internet Protocol (IP) address is a unique numeric address, as opposed to a “reply-to address,” which is often spoofed in spam messages. Spam filters, as they’re called, can operate at the server level and also within an email program that offers this functionality. Email programs can also filter mail into folders as it is received and will normally send a command to the server to delete the collected messages.
Mail servers also commonly have filters that prevent users from sending large quantities of duplicate mail messages to multiple addresses in another attempt to curb spam. Mailing lists are the exception and work with different software that identifies traffic as legitimate. To get around spam blockers, some people try to install mail servers on their computers. Many ISPs consider this a breach of contract, as is often stated in the Terms of Service agreement. Commercial mail servers also use virus filters and trojans.
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