STR: 1. Login to Twitter, go to privacy and request advertiser list 2. Wait until the mail arrives 3. Open the mail in Thunderbird Actual results: In Thunderbird is no attachment shown in the mail. If you open the source there is: ------=_Part_foo_bar Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable some plain text ------=_Part_foo_bar Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable some html text ------=_Part_foo_bar Content-Type: application/pdf; name=twitter_advertiser_list.pdf Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename=twitter_advertiser_list.pdf one line (no line breaks!) of base64 encoded PDF ------=_Part_foo_bar-- Expected results: Thunderbird should show the attachment as other mail clients do. This has been confirmed by multiple users.

(we generally don't leave "new" bugs in untriaged component)

Blame Twitter!

More detail: It's really sad that and internet giant like Twitter can't employ standards-compliant software that would produce valid MIME structure. If you read through bug 1386341 or bug 1367973, you'll find a workaround that will allow you to show all body parts regardless of how badly the e-mail is structured.