On Wed, 23 May 2018 16:57:18 +0000, Pew, Curtis G  wrote:
>> 
>> Why didn't the supplier, as a courtesy to the customer, deliver the file with
>> the needed extension and save that step?
>
>This is just a guess, but maybe some firewalls or other policy enforcing 
>software block .jar files but allow .zip files. If you have a Java VM on your 
>system, .jar files contain executable code and in some circumstances might be 
>executed inadvertently.
> 
And other firewalls block .zip instead (or also).  After all, a .zip might 
contain
anything, including executable code.  Some firewalls have a whitelist.  And I
dealt recently with one that blocked a .eml (Forward as Attachment).

MIME-encode it; strip headers; name it *.txt. or wrap it as *.pdf.  But don't
rely on a filename as defense against malware.  See: "steganography".

-- gil

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