[Mailman-Developers] MM3: Content filter rules

Mark Sapiro mark at msapiro.net
Mon Mar 2 20:15:57 CET 2009

Barry Warsaw wrote:
>So I'd like to solicit your input on how you use the feature, and if  
>you have any ideas for an approach that would be easier to understand,  
>more useful, or both.

My typical list is set up as follows to allow plain text only. List
mail is not signed so I don't have that issue.

filter_content -> Yes
filter_mime_types -> empty
filter_filename_extensions -> default, but irrelevant
pass_filename_extensions -> empty
collapse_alternatives -> Yes
convert_html_to_plaintext -> Yes
filter_action -> Reject

I have one list which is used to discuss the planning for an annual
event (century bicycle ride) which we run as a fund raiser. Since it
is not possible to get all the people involved to understand that
there are alternatives to attaching spread sheets and word processing
documents, this list is set up as above except that pass_mime_types is
set to


This generally works except for one user's misconfigured Microsoft
Outlook/Exchange that attaches a PDF as application/octet-stream.
There's no good way around that (other than fixing the source). We
could accept all MIME types and filter only on file name extension,
but that would accept anything without a name or with a name without
an extension.

In fact, given the nature of this list and its membership, I could
probably accept everything and just collapse alternatives and convert
HTML to plain text and it would be OK.

BTW, as an aside regarding collapse_alternatives, I have seen on a
non-Mailman list, non-compliant posts from a Lotus notes user that
have the text/html alternative preceding the text/plain alternative in
a multipart/alternative part. I don't know what you do about that...

As far as ideas for improvement go, I don't know if anyone actually
uses filter_mime_types. It seems best to "whitelist" what you want
rather than trying to "blacklist" what you don't want. I think we
could probably do without filter_mime_types.

The other confusing point for some users is they have to allow various
multipart/* types in order to allow the sub-parts they want. Possibly
we could do something where you just specify the elemental content
types you want to allow, and we examine all multipart parts implicitly
and accept those elemental sub-parts that are allowed.

Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan

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