1- message text was treated as attachment and remained on the server as either "msg.0.bin" or "msg.0.txt" files. Fixed by testing the part type before urlizing it.
2- some special characters in message id led to the attachment to be considered missing by Sympa.

I had to refactor the code a bit to allow urlizing of nested multiparts.

The detail of urlization treatment is as follows:

1- any multipart/mixed message part will be analyzed to look for urlizable parts,
2- any mulitpart/related message part will be be analyzed to look for multiârt/mixed sub parts,
3- within the multipart/mixed parts, any text/* part whose "Content-Disposition" header is not "attachment" and has a correct Content-Type.charset value is kept untouched,
4- any other subpart is kept on the server an replaced by a download link.