On Wed, 01 Jun 2016 13:58:20 +0800, you said:

Sorry, I mean the mail's content?
I can not read the mail, there's only a *.bin file attached?

You have a defective mail reader, which is unable to recognize
a digital signature.  There's been an Internet standard for that
since 1995, so there's *really* no excuse.

1847 Security Multiparts for MIME: Multipart/Signed and
     Multipart/Encrypted. J. Galvin, S. Murphy, S. Crocker, N. Freed.
     October 1995. (Format: TXT=23679 bytes) (Status: PROPOSED STANDARD)
     (DOI: 10.17487/RFC1847)

Even if your mail reader doesn't understand how to verify a PGP
digital signature, it should at *least* tell you "This was a text
mail with a digital signature I can't handle".

It's 2016.  Even Outlook figured out how to do this a decade ago.
Complain to whoever did your mail software.