ATT File Documentation

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Technical details

Feature	Value
Full name	Web form data file (postdata.att)
File extension	.att
MIME type	text/plain
Format type	Plain text — the field=value pairs a browser submitted
Developer	None — produced by browsers/servers on form submission
Typical filename	postdata.att
Cause	Misconfigured form encoding or missing server-side handler
Header / signature	None — readable text, no magic number
Delivered as	Usually an email attachment
Contents	The data from a single form POST
Open with	Any text editor (Notepad, Notepad++, TextEdit)
Convert to	.txt (rename only) or .csv (manual cleanup)
Other .att uses	Alphacam lathe tools, Creatures game data, mail attachments (separate types)
Related extensions	.txt, .eml, .msg

What is an ATT file (postdata.att)?

The web-form meaning of .att, classically the file named postdata.att, is plain text produced when an HTML form is submitted. When someone fills in a form on a website and clicks submit, the browser packages the entered fields and POSTs them to the server. If the form’s encoding is misconfigured, the raw submitted field=value text can be delivered as a file rather than handled by the server, very often as an email attachment literally called postdata.att. So a postdata.att sitting in an inbox is usually just the readable contents of a web form someone filled out.

There is no format to decode here. The file is plain text with no header, no signature and no container, and you read it directly in any text editor. This article covers that dominant web-form case. The .att extension is short and was never formally claimed, so a handful of unrelated programs reuse it (Alphacam lathe-tool definitions, Creatures game body data, some mail systems’ attachment payloads). Those are separate file types identified by where the file came from, not by anything inside a postdata.att.

Why a form submission arrives as a file

A normal HTML form posts data with enctype="application/x-www-form-urlencoded" (or multipart/form-data for uploads), and the server-side script reads it and does something useful. A postdata.att appears when that chain breaks in a specific way. If the form’s enctype is set to a plain-text type such as text/plain, or the page is configured to email submissions instead of processing them, the browser hands over the submission as a plain-text blob. Mail and web software that receives an unrecognised text payload commonly saves it with a generic .att (“attachment”) name. The result is that the person running the form, or the person the form emails, receives the field values as an attachment rather than seeing them handled on the site.

The important consequence for a reader is that this is a website bug, not a problem with your computer. Nothing is wrong with the file or with the machine that received it; the fix belongs on the site, in the form’s encoding or its missing server-side handler.

What the text inside looks like

Open a web-form .att and you see the submitted fields and their values as readable text, typically one submission per file. Depending on the encoding, the pairs may be separated by line breaks or joined with & as in a URL query string:

name=Jane Smith
email=jane@example.com
subject=Order enquiry
message=Please confirm my order #4471.

Because it is already text, there is no real conversion involved. Renaming postdata.att to postdata.txt simply makes text applications open it by default; the bytes do not change. If a file holds many field=value lines and you want them in a spreadsheet, reformat the lines into comma-separated rows by hand or with a find-and-replace, save as CSV, then open in Excel or LibreOffice Calc. There is no automated converter because the layout varies from form to form, so treat it as manual cleanup rather than a tool.

References

• MDN — Sending form data (enctype and POST)
• FileInfo — .ATT file extension
• File.org — ATT file: how to open

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