[svlug] Email length

J C Lawrence claw at kanga.nu
Mon May 15 16:27:38 PDT 2000


On Mon, 15 May 2000 12:59:02 -0700 
Derek J Balling <dredd at megacity.org> wrote:

> At a fundamental level, I do not agree with the MTA caring about
> the content of the DATA segment at any time. However, I can also
> acknowledge that this is an area that no good RFC has been written
> to cover yet, so I can accept that there may need to be some
> flexibility on this front in the future.

If you consider the MTA as discrete from the feature of allowing the
postmaster to implement mail handling policies (which are external
to the MTA, but the which the MTA supports via
callouts/filters/whatever), then this whole debate pretty well
vanishes.  The MTA doesn't dick with message bodies.  The MTA
supports the functionality of filters and other devices by which,
among other things, an Admin can contrive to dick with message
bodies should he so wish.  

> BUT -- There is a difference between ALTERING the content, and
> SCANNING the content.

We were discussing the active removal of active content from
messages during transit...

> If the MTA is going to accept a message, it should accept it as-is
> with no modifications (except to the headers as specified in the
> appropriate RFC).  If the MTA decides - for whatever reason it
> chooses - to deny the message, then it may do so, but MUST do so
> in the appropriate manner: sending a 500-series response code to
> the sender indicating permanent message failure and the reason for
> such failure. The sender MUST be aware of the status of the
> delivery success/failure. Dropping the message on the floor is not
> an acceptable solution.

> However, there are a few caveats: 1.) There are some (poorly made)
> MTA's which do not properly handle receiving a 500-series failure
> AFTER they have delivered the DATA segment.  Depending on the MTA
> in question, some will not see it as an error, but see it as
> success and not generate a DSN for the sender. They may also
> continuously retry to send the message. (Not seeing it as
> "Success" but missing that it is a "failure")

Suffice to say, I hate MTAs like that, having more than once been at
the receiving end of their idiocy when bandwidth was a precious
commodity.  Some of the MS "mail servers" used to fit this
description.

> 2.) Most schemes designed to find attachments in messages are not
> too well-thought-out and will false-positive more than is proper.

Sadly true.

-- 
J C Lawrence                                 Home: claw at kanga.nu
----------(*)                              Other: coder at kanga.nu
--=| A man is as sane as he is dangerous to his environment |=--





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