Comment 7 for bug 593459

I made further tests with the following result: I took such a PDF I got (offering only the save option) and sent it as new mail with attachment to myself using Thunderbird.

Result: Open option available! - So it does not depend on the PDF itself. I assume that it depends on the mailer how it packs the mime message. Did further investigation and found the following difference:

Attachment header in mime Test-Message that is working:
Content-Type: application/pdf;

 name="#31161-v1-Programmierung_RepCheck.pdf"

Content-Transfer-Encoding: base64

Content-Disposition: attachment;

 filename="#31161-v1-Programmierung_RepCheck.pdf"

Attachment header in Original received mail:
Content-Type: application/octet-stream;

 name="#31161-v1-Programmierung_RepCheck.pdf"

Content-Transfer-Encoding: base64

Content-Description: #31161-v1-Programmierung_RepCheck.pdf

Content-Disposition: attachment;

 filename="#31161-v1-Programmierung_RepCheck.pdf"

It looks like a difference in specified Content-Type. The original mail I got, was produced with MS Outlook 2007.

HTH.