Content-Disposition

The Content-Disposition, if present, is usually either "inline" or "attachment". For attachments, a filename attribute should be present. For inline message parts, a filename may still be present if the message part is truly an attachment that can both be displayed inline and saved to a file.

Two common ways of presenting multipart email messages are as a main document with a list of separate attachments, and as a single document with the various parts expanded (displayed) inline. The display of an attachment is generally construed to require positive action on the part of the recipient, while inline message components are displayed automatically when the message is viewed. A mechanism is needed to allow the sender to transmit this sort of presentational information to the recipient; the Content-Disposition header provides this mechanism, allowing each component of an email to be tagged with an indication of its desired presentation semantics.

Example:

Content-Disposition: attachment; filename="something.zip"