Apple Mail sends attachments as inline are are marked as alternate views and the name of the attachment is lost.

The behavious can be changed http://katiefloyd.me/blog/get-rid-of-inline-attachments-in-apple-mail otherwise an attachment will look like this:

Content-Type: multipart/mixed; boundary=Apple-Mail-2--769176039

--Apple-Mail-2--769176039
Content-Transfer-Encoding: 7bit
Content-Type: text/plain;
 charset=us-ascii

Hello
--Apple-Mail-2--769176039
Content-Disposition: inline;
 filename=" xxx.pdf"
Content-Type: application/pdf;
 name=" xxx.pdf"
Content-Transfer-Encoding: base64