I looked around and this is the definition I found -
QUOTE
Web Form Data (POSTDATA.ATT)
If the file is named POSTDATA.ATT then most likely the file contains the results from a Web form. This will be an ASCII text file with a bunch of strange characters betwee the data fields. You can open the file in any text editor and read past all the junk or use a tool such as Post Data Spider to just show the data.
There's a very good site dedicated solely to file extensions. Its called
FILExt - The File Extension Source and can be accessed at:
http://www.filext.com/Other than that, there's always Google search

A simple ".att file" would have fetched you a whole bunch of results..
Click on this link for the search results:
http://www.google.com/search?q=.att+file&s...:en-US:official
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