User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_5_8; en-us) AppleWebKit/533.16 (KHTML, like Gecko) Version/5.0 Safari/533.16 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.8) Gecko/20100802 Lightning/1.0b2 Thunderbird/3.1.2 Just-upgraded to 3.1.2, and can no longer open attachments containing CSV (comma-separated values) part. Before upgrade to 3.1.2, used to open Excel. Reproducible: Always Steps to Reproduce: 1. Receive a multipart-mixed email with a "text/plain" part and "application/octet-stream" parts 2. Double-click to open the attachment 3 [review]. Actual Results: Attachment is displayed by TB as text. Expected Results: Attachment will be opened by Excel First part header: Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: quoted-printable [contains "body" of message] Second part header: Content-Type: application/octet-stream; name="P1YYMMDD.CSV" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="P1YYMMDD.CSV" May have same cause as Bug 587660. Have full email available. [again selected "Windows XP" as platform because I'm not sure what "NT 5.1" is] [severity set at "normal", but if parsing "application/octet-stream" is broken, should be higher]

This is INVALID as Content-Type: application/octet-stream; name="P1YYMMDD.CSV" clearly doesn't say something like application/vnd.ms-excel. Mike, does it work better is the attachment is named "P1YYMMDD.csv" ?

I don't think it's invalid, as -- according to the user -- this used to work. From what I can tell, there IS code to handle "digging into" application/octet-stream attachments and deciding what to do based on the filename extension; see: http://mxr.mozilla.org/comm-central/source/mailnews/mime/src/mimei.cpp#850 I don't know for sure that code ever gets involved when trying to display/save attachments, but I don't know what else it purpose would be. I tried to figure out what MIME type would be returned based on a particular filename extension, but the "mapping" of extension-to-MIME-type is OS and user-dependent. Someone more familiar with where execution would proceed, given a particular filename extension, could probably determine if there were any changes in that area between early 3.x and 3.1.2. If the filename/extension is case-sensitive, I'd say that's a bug (at least by my cursory examination of RFCs 2183 and 1521). Finally, "This is INVALID as [...] clearly doesn't say something like application/vnd.ms-excel." No, it doesn't -- but it doesn't say "application/vnd.thunderbird", either. If TB isn't supposed to try to open a compatible "AppHelper", then it certainly shouldn't display the attachment as text; the user should be asked if he/she wants to save the file.

I have the same problem : I want to open csv files with excel and txt files with notepad. But both attachments are mime type Text/Plain. So Thunderbird always use the program associated with txt files. The only solution I found is not to associate txt files with notepad. Each time I want to open a txt file, I have to confirm the message box (without prompting the option always do this action). I tried to manually modify the file mimeTypes.rdf in my profile. But I don't find a solution. If someone knows a better solution, I will use it.

This is the same as bug https://bugzilla.mozilla.org/show_bug.cgi?id=300168

I've found a work-around. As noted above, the problem is when a mail client marks the attachment as Text/Plain. Outlook handles csv attachments correctly (open in Excel) because Excel is a Microsoft product, so it presumably "just knows". To fix this for Thunderbird, the client must send the csv attachment as Content-Type: application/vnd.ms-excel. Thunderbird, as a client, DOES do this. I am using mail(x). To make this work with the mailx client, the following entry must exist in /etc/mime.types: application/vnd.ms-excel csv That did the trick for me. Other clients (e.g. mutt), also have mime.type settings.