Layers of an E-mail

this single layer format is because email is meant for a communication, not as a base for an application.
email should only be plain text.

What time is your homework due in then?

By the way, they are some of the layers of the OSI networking model.

Do I get a cookie?

It is a homework problem. You need to solve the issue alone, otherwise nobody will want to work with you in the future. The best thing to do is to learn by example... or use the web as reference. The internet is the #1 tech tool available.

If you are asking this, as some people have suggested, because you need to know this for a class then you should be able to figure it out for yourself. Look at the OSI Network Model. Figure out how each layer is accomplished. Then figure out what parts are implemented in the email application. If this is for a class then maybe your teacher wants you to do exactly what I have suggested. This would test your understanding of how networking is implemented and how applications use the networking software.

Also condider this: Email doesn't always have to use a network. Sometimes the sender of the email and the receivers have their email account on the same server.

The layers of the OSI model are Application, Presentation, Session, Transport, Network, Data Link, and Physical.

When an email is sent over the internet, it uses SMTP (Simple Mail Transfer Protocol).

These protocols will format the document in accordance with the standards set by the protocol. (You may want to or not check it out, but there's no need).

Next, the Application layer, which Outlook Express resides in will create a packet and attach a header to the email address. This happens all the way down to the physical layer till it's ready to be sent out on the internet.

The reverse happens over the other end once the packet has travelled through ISPs, routers, switches, etc., till it reaches the desired server.

IMAP4 protocol on the server subnet you are trying to reach will store it in the server till the user goes to check his email.

The reverse will happen at that moment he opens Outlook Express and the computer OS will go through the OSI model in reverse till it removes all the headers and checksums until it reaches the Application layer (This takes milliseconds).

Finally, the application uses the SMTP to decode the message and the user will be able to read it.