User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.7) Gecko/20050414 Firefox/1.0.3 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.7) Gecko/20050414 Firefox/1.0.3 Admitted the attachment 182156 [details] ("corruptSigned.eml") is based on a bug in microsoft outlook (send a signed message, open for resend and then disable signing and send again). But I guess even if Thunderbird receives corrupt MIME, it should robustly display what it reasonably can and not dream up attachments that do not exist. Reproducible: Always if as per bug 292329, you also have difficulties opening the attached message from the disk, just attach it as .eml and mail it to yourself. Then bug has slightly different features: when opening the attached corruptSigned.eml, it will recursively show itself as attachment...

Using Thunderbird version 1.0.2 (20050317)

This is also a dupe; it's the same bug as 292329. The message is not corrupt, by the way, it just has an unusual Content-Type header. *** This bug has been marked as a duplicate of 182627 ***

maybe "corrupt" is the wrong word for it, but AFAIK a "quoted-printable" should always be together with a "charset", otherwise, e.g. Umlauts get wrong. BTW, having both in Outlook and Thunderbird "?" or "ü"instead of "ü" was how we started to notice that something is "unusual"

It's true that the message should have a charset, since it's encoded with UTF-8 and the default (if no charset specified) is US-ASCII. It's also true that in Thunderbird, the "Universal Autodetector" is not available (bug 261485). However, that has nothing to do with the display of the "attachment."

also, declaring a message <<smime-type=signed-data; name="smime.p7m">> and neither adding a signature nor using the encodings tyically found with p7m is kind of misleading (admitted, thunderbird does detect that it's not signed)