(abbreviated "e-mail" or, often, "mail") is a store and forward method
of composing, sending, storing, and receiving messages over electronic
"e-mail" (as a noun or verb) applies both to the Internet e-mail system
based on the Simple Mail Transfer Protocol (SMTP) and to intranet
systems allowing users within one organization to e-mail each other.
workgroup collaboration organizations may use the Internet protocols for
internal e-mail service.
E-mail is often used to deliver
bulk unwanted messages, or "spam", but filter programs exist which can
automatically delete most of these.
Messages are exchanged between hosts using
the Simple Mail Transfer Protocol with software programs called mail
transport agents. Users can download their messages from servers with
standard protocols such as the POP or IMAP protocols, or, as is more
likely in a large corporate environment, with a proprietary protocol
specific to Lotus Notes or Microsoft Exchange Servers.
Mail can be stored either on the client, on the server side, or in both
places. Standard formats for mailboxes include Maildir and mbox. Several
prominent e-mail clients use their own proprietary format and require
conversion software to transfer e-mail between them.
When a message cannot be delivered, the recipient MTA must send a bounce
message back to the sender, indicating the problem.
Spamming and e-mail worms
The usefulness of e-mail is being threatened by three phenomena:
spamming, phishing and e-mail worms.
Spamming is unsolicited commercial e-mail. Because of the very low cost
of sending e-mail, spammers can send hundreds of millions of e-mail
messages each day over an inexpensive Internet connection. Hundreds of
active spammers sending this volume of mail results in information
overload for many computer users who receive tens or even hundreds of
junk messages each day.
E-mail worms use e-mail as a way of replicating themselves into
vulnerable computers. Although the first e-mail worm affected UNIX
computers, the problem is most common today on the more popular
Microsoft Windows operating system.
The combination of spam and worm programs results in users
receiving a constant drizzle of junk e-mail, which reduces the
usefulness of e-mail as a practical tool.