Hi,

I recently received a multipart email with one of the parts being a pdf but the
part was not marked with "Content-Disposition: attachment". This let to notmuch
not adding tag:attachment to it.

The sender assured me that he used Outlook 2013 but I can't reproduce the
problem myself as I dont have microsoft products at hand. But if Outlook 2013
indeed adds attachments without setting "Content-Disposition: attachment", then
maybe the problem of notmuch not recognizing them as such is more severe?

The question is also what to do about it and how to detect attachments of this
kind. Apparently Thunderbird detects attachments that dont say
"Content-Disposition: attachment" but I did not try to figure out what its
heuristic is. Also the microsoft exchange server web client is able to figure
out that this part is supposed to be an attachment. What do other MUAs do?

So how to create a good heuristic? Using the Content-Type? In my case, the
supposed attachment was "application/octet-stream" for which it is probably
unambiguous that it is an attachment and not inline?

Alternatively, how about making attachment detection configurable so that
everybody is free to decide himself what he wants to be treated as attachment?

cheers, josch