Thanks for your suggestion, here is the output of od -c before and after

Before:
0001740   d   u   c   t   C   o   d   e   =   4   -   %   2   0   I   
+%
0001760   2   0   c   a   s   e   s   &   P   r   o   d   I   D   =   
+2
0002000   0   2   &   D   i   s   p   g   r   o   u   p   =   1   &   
+C
[download]

After:
0001740   o   d   u   c   t   C   o   d   e   =   4   -   %   2   0   
+I
0001760
0002000              \0   a   s   e   s   &   P   r   o   d   I   D   
+=
[download]

I have cc'd the email to the inbox of autotasks, and was able to see the file in ascii text. It does in fact seem to be the perl script that is mangling the file, not the sending application.
As far as the mime type goes, I dont think that is affecting it as the mime type for the Google file is the same as the one for the overture.txt file.
Do you think that maybe printf is finding the %20 or whatnot in the file and interpereting it as binary? I am going to try a regular print, and get back to you.