How many times have you tried to email a co-worker or colleague an executable or batch file that is desperately needed and you get a message such as:

"A message that you have sent could not be delivered to one or more recipients. This is a permanent error. The following address failed … Illegal Attachment"

There are a couple tricks I use such as renaming the file extension.  For instance say I want to send the System Internals for Windows application to a co-worker.  Rename the file from SIW.EXE to SIW.EXX 

When renaming the file you will get a warning message just click yes.

This should allow the file to go through then the recipient of the file can rename it back to SIW.EXE and launch the application.  Some filters are more smart than others.  Another thing way is to zip the file and rename it to SIW.ZI_  

Of course always verify the person sending you the file is reputable and never open attachments you were not expecting.  If you know of any other tricks to use please feel free to comment!