An attachment is not the body

Answer An attachment is not the body. RFC 2183 defines the Content-Disposition header, which tells a mail program whether a part of the message should be displayed inline or treated as an attachment. Inline means show it with the message. Attachment means handle it as a separate file. The header is a presentation instruction. It does not make the file into the letter, and it does not make an open of the file into a click on your offer.

The note that started this: RFC 2183, Content-Disposition Header Field, RFC 2183.

Solo ads sometimes arrive as a short note plus a document. The note says the good part is in the file. The reader has to trust a stranger enough to open a file. Many will not. The ones who do are performing a different act from clicking a link in the letter. If you are hiring best solo ad vendors, ask to see the creative as the reader sees it, letter first, file second, before you approve the send.

MIME already lets a message hold multiple parts. Disposition is the label on a part about how to present it. A part can be a picture the letter needs in order to make sense. A part can be a spreadsheet nobody asked for. The label tells the program which hope the sender had. The program can ignore the hope. Webmail, in particular, makes its own choices about what to show. A seller who promises the attachment will display a certain way on every client is promising a park they do not control.

What does Content-Disposition describe?

RFC 2183 defines a header that says whether a message part should be shown inline or treated as an attachment. The header describes presentation. It does not turn an attachment into the body of the letter.

Presentation is the arrangement on the screen. The body of a mail, in the ordinary sense a buyer means, is the words the person can read without an extra step. A disposition mark can try to put an image in that flow. It can also try to park a file at the side. Knowing which one the creative uses is part of knowing what you bought. Ask for the disposition in a sentence. Is the offer in the letter, or is the letter a cover note for a file?

Parameters on that header can suggest a filename. This note will not catalog them. A filename is a suggestion. It can be wrong, odd, or the same as last week's file. Judge the creative by opening it in a plain mail client, not by the name in the quote.

• The offer is visible in the letter without opening a file.
• Any file is named in the quote, with its type.
• The seller does not call a file-open a click.
• The preview matches what a plain client shows.

Is an attachment the same as the email body?

No. The body is the message the reader is meant to read in the letter. An attachment is a part marked to be handled as a file. A solo ad that hides the offer in a file is a different object from a letter with a link.

Hiding the offer is sometimes laziness and sometimes a hope that the file will bypass a glance. Readers are not obliged to cooperate. Filters also get a vote, and a vote about attachments is often stricter than a vote about a short letter, because files are how a lot of unwanted software travels. You do not need a horror story to make the buying decision. You need the creative in the form the reader gets.

A letter with a link can be judged in one screen. A letter that demands a download asks for a second decision. Price the second decision. If the seller's past results depend on people opening files, those results belong to file-openers. Your next offer may not attract the same patience.

Will a click tracker see an attachment open?

Usually no. A tracker on a web link sees a request to that link. Opening a file in a mail program is a different event. If the only action is the file, ask how the seller counts a response.

This is a measurement gap, not a dare to hide the offer where the tracker cannot see it. If you cannot see the response, you cannot tell a good list from a silent one. Put the action on a link you can count, inside the letter, and keep any file as a support for people who already clicked. Then a quiet day is a quiet day, not a mystery about whether the file was opened on a machine you will never audit.

RFC 2183 gave programs a way to tell inline from attachment. Use the distinction on the order. The body is the letter. The file is the file. Pay for the one the reader can actually finish.