MS Outlook cannot recognize PDF format 1.7 when sending it as an attachment. Therefore it's sent as: Content-Type: application/pdf; Content-Transfer-Encoding: quoted-printable When receiving such an e-mail under Linux (Thunderbird), the PDF content is being parsed as a plain text and converted. This results in a corrupted file loosing all the bytes 0x0a (LF) which are being removed by the EOL conversion. It's definitely a problem of Outlook which is IMO hard to fix and deploy. Is there a way to fix that on Thunderbird's site?