ietf-mta-filters
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Should the exists header match a header with no "content"

2001-04-18 05:05:28
What exactly does it mean for a header to exist in an email?  If the name of 
the header exists, but the content is blank does this header exist or not?

ie suppose I have a script:
  if not exists "From" {
      discard;
  }
Then obviously it should discard:

   Date: Tue, 1 Apr 1997 09:06:31 -0800 (PST)
   To: roadrunner(_at_)acme(_dot_)example(_dot_)com
   Subject: I have a present for you

   Look, I'm sorry about the whole anvil thing, and I really
   ....
   great birdseed over here at my place--top of the line

and not discard:


   Date: Tue, 1 Apr 1997 09:06:31 -0800 (PST)
   From: coyote(_at_)desert(_dot_)example(_dot_)org
   To: roadrunner(_at_)acme(_dot_)example(_dot_)com
   Subject: I have a present for you

   Look, I'm sorry about the whole anvil thing, and I really
   ....
   great birdseed over here at my place--top of the line

but should this discard the following message?

   Date: Tue, 1 Apr 1997 09:06:31 -0800 (PST)
   From:    
   To: roadrunner(_at_)acme(_dot_)example(_dot_)com
   Subject: I have a present for you

   Look, I'm sorry about the whole anvil thing, and I really
   ....
   great birdseed over here at my place--top of the line

I know I could change my exists test code to catch "empty" headers, but does 
anyone know if there are any headers in existence that may legitimately not 
contain any "data".

I know I could probably hunt for several hours in the RFCs to find the answer 
to this one, but though I would cash in on you experience.  Besides, the 
traffic on this list has been quite low these days :o)

Nigel
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