Overview
SMTP, POP3 and IMAP are TCP/IP protocols used for mail delivery. If you
plan to set up an email server such as hMailServer, you must know
what they are used for. Each protocol is just a specific set of
communication rules between computers.
SMTP
SMTP stands for Simple Mail Transfer Protocol. SMTP is used when email is delivered
from an email client, such as Outlook Express, to an email server or when email is delivered from
one email server to another. SMTP uses port 25.
POP3
POP3 stands for Post Office Protocol. POP3 allows an email client to
download an
email from an email server. The POP3 protocol is simple and does not
offer many
features except for download. Its design assumes that the email client
downloads all available email from the server, deletes them from the
server and then disconnects. POP3 normally uses port 110.
IMAP
IMAP stands for Internet Message Access Protocol. IMAP shares many
similar features with POP3. It, too, is a protocol that an email
client can use to download email from an email server. However, IMAP
includes many more
features than POP3. The IMAP protocol is designed to let users keep
their email
on the server. IMAP requires more disk space on the server and more CPU
resources than POP3, as all emails are stored on the server.
IMAP normally uses port 143.
Here is
more information about IMAP.
Examples
Suppose you use hMailServer as your email server to send an email to bill@microsoft.com.
- You click Send in your email client, say, Outlook Express.
- Outlook Express delivers the email to hMailServer using the SMTP protocol.
- hMailServer delivers the email to Microsoft's mail server, mail.microsoft.com, using SMTP.
- Bill's Mozilla Mail client downloads the email from mail.microsoft.com to his laptop using the POP3 protocol (or IMAP).
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