well, you would need to have a database table that would relate each code to each file, for example:
+--------+---------+-----------+
| codeID | code | fileName |
+--------+---------+-----------+
| 1 | 1234567 | file1.zip |
+--------+---------+-----------+
| 2 | abcdefg | file2.zip |
+--------+---------+-----------+
| 3 | 1234abc | file3.zip |
+--------+---------+-----------+
| 4 | abc4567 | file4.zip |
+--------+---------+-----------+
then in the email, add a link to your download page
<a href="http://mydomain.com/download.php">Doanload your file</a>
on the download page, add the form with a text box and submit button.
create a recordset that will filter the code column on the code entered in the text box.
In the Download file server behavior, set the file name to use the fileName column of the recordset and trigger to use any form post.
