For identifying the type of data contained in a file based on its extension,Multipurpose Internet Mail Extension, a standard system is used.
A D V E R T I S E M E N T
To send binary files across the Internet as attachments to e-mail messages,MIME protocol is used and it is an Internet protocol.
This includes graphics, video, sound and photos files, and formatted text documents.
Common MIME Data Types
Although the top-level MIME media types correspond to basic concepts that all users would understand, not all subtypes fall under the obvious media category and those that are associated with specific application software, for instance, may be classified as application types rather than text, image, or audio, despite being widely available over the Internet.
Often these data types require a browser plug-in before their contents will be correctly processed when visiting a Web site, or the client browser might ask you to specify which application is associated with file extension or that subtype.
The following table describe most common MIME text types:
Common Format Name
US ASCII text with no format tags
HyperText Markup Language
Defines World Wide Web pages
Rich Text Format
Vendor-independent word processing file
type with some formatting capabilities
ps, .ai, .eps
Print and display format
Portable Document Adobe's PDF
Format used by Acrobat for
platform-independent display and printing
New Header Fields in MIME
MIME defines the following new header fields:
MIME-Version, which uses a version number to declare that a
message conforms to MIME standard.
Content-Type, which can be used to specify the subtype and
type of data in the body of a message and to fully specify the
encoding of such data. It includes also a subtype option. The seven
Content-types specified are:
Text - to represent textual information in a number of
Image - for transmitting still image (picture) data.
Audio - for transmitting audio or voice data.
Video - for transmitting video or moving image data.
Message - for encapsulating a mail message.
Multipart - to combine several body parts, possibly of
different types of data, into a single message.
Application - to transmit application data or binary
Content-Transfer-Encoding, which specifies how the data is
encoded to allow it to pass through mail transports having data or
character set limitations.
Content-ID (optional), which enables labeling bodies, thus
allowing one body to reference another.
Content-Description (optional), which enables associating
descriptive information with a body.
IMAP(Internet Message Access Protocol)
A protocol allowing a client to manipulate and access electronic mail messages on a server and it permits manipulation of remote message folders (mailboxes), in a way that is functionally equivalent to local mailboxes.
IMAP includes operations for creating,deleting, and renaming mailboxes; checking for new messages; permanently removing messages; searching; and selective fetching of message attributes, texts, and portions thereof. It does not specify a means of posting mail; this function is handled by a mail transfer protocol such as SMTP.
IMAP Basics - What it is, and what it can do.
For anyone who has a requirement to access multiple separate mail accounts
that reside on different machines, access to email becomes problematic and many
mail systems use the tried and tested POP3 protocol. POP3 client applications
download the mail from the server, and store it on the client computer. Most
clients store mail in their own format, making it inaccessible by other mail
programs, and most machines which run POP3 clients are desktops, which are
rarely on 24/7, further reducing access to the mail once it has been downloaded.
The IMAP protocol attempts to remedy some of these problems and
the strength of IMAP lies in online and disconnected operation. Unlike POP3, mail is not copied
from the server and then deleted - instead, IMAP clients manipulate the mail on
the server, and permit access to remote, server hosted mailboxes as though they
were local resources.
An IMAP mail system has a number of immediate advantages for users which are given below:-
As all mail is stored on the server and changing mail client becomes the
work of seconds - all that is required is to configure a new IMAP client
with the IMAP account details.
An IMAP client can easily be configured to view the multiple mailboxes in
physically separate servers.
Multiple IMAP clients can be used by each user and this makes implementing
a webmail solution for roaming users a simple task.
IMAP maintains the message status flags on the server for read, answered,
IMAP allows the idea of shared folders and this makes it easier to
implement generic email accounts for an organisation, and then allow
multiple users to access those accounts.
Many implementations also allow server side filtering of mail and this can
be an extremely useful feature when users are accessing their mailboxes
through different email clients.
Comparing IMAP and POP
What does it stand for?
Post Office Protocol
Internet Message Access Protocol
Which protocol would suit me best?
If you access mail using only one computer e.g. your office PC or a
If you want to access your mail from multiple computers or
Which mail programs can I use?
All mail programs or clients have POP
Many mail programs now have some IMAP capability but you
will generally need to use the latest version of one of the more popular
programs such as Netscape Messenger, Eudora or Outlook Express to ensure
that you can use full IMAP features. You will also be able to access
your mail via a web page using any web browser.
Some Common Tasks:
Check for incoming mail
By default, incoming messages are
transferred to your local machine when you check your incoming mail.
Only new messages are available if you connect to the server using a PC
other than your normal one. You are connected to the server only for the
transfer of messages.
By default, incoming messages stay on the server when
you check your mail - only headers are transferred with full messages
only downloaded when selected for reading. All your messages are always
available no matter where or how you connect to the server. You remain
connected to the server whilst you deal with mail but some clients allow
for off-line working.
Read and respond to mail
Reading and responding to messages is done
on your local machine.
You can read and respond to messages
directly on the server but you can also read and respond to messages on
your local machine, after downloading for offline working (depending on
client). When you reconnect, your mailboxes are resynchronised to
reflect the changes you have made.
Create mailboxes for storing messages
Creating mailboxes can be done only on your
You can create mailboxes directly on the
server. By default, an Inbox is automatically created on the server when
you begin using IMAP. The Inbox functions as the master mailbox (or
folder) as well as the mailbox for incoming messages. All other
mailboxes, including a trash box, need to be created within the Inbox.
Move messages in and out of mailboxes
You can move messages in and out of
mailboxes only on your local machine.
You can move messages in and out of
mailboxes on the server and on your local machine.
Transfer messages from local machine to
server and vice versa
You cannot transfer any messages from your
local machine to the server. Messages are automatically transferred from
the server to your local machine when you check your incoming mail.
You can transfer individual messages from
mailboxes on your local machine into mailboxes on the server and vice
Delete selected messages on the server
When using some clients (e.g. Eudora), if
you specified to leave messages on the server, you can delete individual
messages left there.
You can delete individual messages and
groups of messages directly on the server as well as on your local