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With David's permission, I quote his message
On Mar 2, 2009, at 1:50 PM, David Champion wrote:
This is a crazy idea I haven't really thought through, and completely tangent to what you're asking, but what about implementing a Milter interface (the MTA component, not the filter component) in Mailman and adopting its semantics?
Then Mailman could take advantage of an existing framework with many instances in the field already, while limiting the use of those
filters to Mailman (not the whole MTA) and being completely independent of whichever MTA you're indeed using.The pymilter project makes writing Milter filters in Python rather
easy, so that Mailman-specific milters can be contributed and distributed
with Mailman. http://www.bmsi.com/python/milter.html
This occurred to me too, so let's explore it.
MM3 has a lot of plugin points, and content filtering could definitely
be one as well. For example, I could imagine a filter such as "leave
nothing but the first text/plain", "strip out all word documents",
etc. implemented as Python modules. Some would come with stock MM3,
others could be added by the site administrator. In fact, I think the
current mime_delete.py handler could be implemented as a plugin
(though I'm not sure you'd want to ;).
The advantage of a plugin architecture here is that I think it is
simpler to implement, understand, explain, and skin. The disadvantage
is that the individual plugins would be less flexible, and you'd need
a site administrator to add third party plugins.
I'm not sure that the milter API is quite appropriate for Mailman,
which has a much different architecture than an MTA. For example, it
doesn't make sense for Mailman to expose SMTP callbacks since that
will have happened long before Mailman gets its paws on the message.
But something /like/ this could make a lot of sense.
Barry
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