How do you forward an attachment from another email?

How does email client sent attachment to another email client. For example if i sent a song from yahoo mail to hotmail, how does it work?

• Specifically i want to know how much of yahoo server bandwidth is used if i forward a mail containing a song of 4 MB to another email client.

• Answer:

  Attachments are part of the email itself. When you add an attachment, that attachment is appended to your email content in a way that is hidden when you're reading the email, but is visible to your email client, so that you're able to download the attachment or perform other meaningful actions on it. If you're sending a 4MB audio file from Yahoo! Mail to an external mail service, you should expect that somewhere between 4-5 MB of storage will be required on the receiving end. Total bandwidth consumed transferring the message may vary, but that amount of space will be required for each recipient to which you're sending that message. So try to avoid sending files over 1 MB to more than 2-3 recipients. If you need to do that, consider a file hosting service such as Dropbox or http://Min.us, and send people a download link for the file, rather than an attachment.