I don't understand this issue myself.  I didn't get Madhav's recording myself (gmail user).  But the pattern of who does and who doesn't get the attachments is not obvious.

The Mailman software uses the following rules for attachments:

Policies concerning the content of list traffic.

Content filtering works like this: when a message is received by the list and you have enabled content filtering, the individual attachments are first compared to the filter types. If the attachment type matches an entry in the filter types, it is discarded.

Then, if there are pass types defined, any attachment type that does not match a pass type is also discarded. If there are no pass types defined, this check is skipped.

After this initial filtering, any multipart attachments that are empty are removed. If the outer message is left empty after this filtering, then the whole message is discarded.

Then, each multipart/alternative section will be replaced by just the first alternative that is non-empty after filtering if collapse_alternatives is enabled.

Finally, any text/html parts that are left in the message may be converted to text/plain if convert_html_to_plaintext is enabled and the site is configured to allow these conversions.


  • filter types: none, so nothing should ever be discarded by this criterion.
  • pass types are as follow, and should cover most types of file that people want to attach: 
    multipart
    text/plain
    text/html
    text/xml
    application/pgp-signature
    message/rfc822
    image/jpeg
    image/pjpeg
    application/pdf
    image/gif
    image/tiff
    application/msword
    application/x-dvi
    application/postscript
    application/x-tex
    application/vnd.oasis.opendocument.text
    application/x-vnd.oasis.opendocument.text
  • Files with the following extensions are removed:
    exe
    bat
    cmd
    com
    pif
    scr
    vbs
    cpl
  • collapse_alternatives is set to "no"
  • convert_html_to_plaintext is set to "no"
Now, mp3 files are not included in the pass types.  That would, I think, explain why Mailman didn't forward Madhav's voice recording.  And yet some people received it.  That's baffling.

I've now added audio/mpeg to the "pass types", so mp3s should get through in future.  Also audio/ogg.  I haven't added /wav files because they are typically unreasonably huge.


Dominik Wujastyk, for the INDOLOGY committee.