You can attach any file smaller than 20MB.

Files with the following extensions can be directly attached:

• Images
  • gif, png, jpeg, jpg, tif, tga
• Documents
  • doc, xls, ppt, txt, csv, vsd, mpp, pdf, html, htm
• Archives
  • zip, rar, gtar, gz, tar, ace

For all other types of files: First archive them into one of the above 'Archive' formats (using software like WinZip or 7-Zip) - and then attach them into Accompa.