The only workaround I can think of is to zip them up and send and receive zip files instead of .pl/.pm files. I do not use Outlook or Outlook Express so I couldn't help you with the registry keys.

Update:
There seems to be some information here.

Just a tongue-tied, twisted, earth-bound misfit. -- Pink Floyd

In reply to Re: How do I get Outlook Express not to treat perl scripts as potential viruses by data64
in thread How do I get Outlook Express not to treat perl scripts as potential viruses by rinceWind

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