MIME The Multipurpose Internet Mail Extensions

While  the message  headers described in are satisfactory for sending  ordinary  ASCII text they are  not sufficiently Reich for multimedia messages(for example messages with  images audio and video) or for carrying  non ASCII  text formats ( for  example  characters used by language other then English ). To  send  content  other then  ASCII text the sending user agent must include additional headers  in the message.

MIME  defines  five  new message headers as show in table 8. These are described  below  one by one:

1.MIME version simply  identifies the version of MIME.

2.The content description Header is an ASCII string  telling  what is  in the message .

3.The content id heard identifies the content.

4.The content transfer  encoding : Header alerts the receiving user agent that the  message  body  has been ASCII encoded and indicates the type of encoding used. Thus when  a user agent receives a message with these two header if first  uses the  value  of the content transfer encoding heard to convert the message body  to its original non ASCII form and then  uses.

5.The content type header to determine  what  action it should  take on the message  body. Let  take  an example of MIME  message.

From : heena@yahoo.

To : harish@rediff. Com

Subject : Picture of monalisa

MIME : Version  : 1.0

Content  transfer encoding  : base 64

Content   - Type  image  jpeg

 Base 64 encoded date ................

.....................................................

............................ base 64 encoded data)

We  observer form  the above  MIME message  that heena user agent  encoded the JPEG  image  using  base 64 encoding. This is one of the  several encoding techniques  standardized  in MIME for conversion to  an acceptable 7 bit  ASCII format.

When  Harish  reads his mail  with his  user agent his user agent operates on this game  MIME message  when Harish use agent observes the content transfer encoding base64 header line. It proceeds to decode the base  640 encoded message body.

The message  also  includes a content type  image jpeg  header line his  indicates to Harish  user agent that the  message body  should be JPEG decompressed. Finally the message includes the MIME version. Header which indicates the MIME version that  is being  used. In  particular  after the message  header  there is  blank  lien and  then the message body.