Gnus not recognizing encrypted message

[Lloyd Zusman <ljz@asfast.com>]

Normally, if someone sends me an encrypted message, Gnus recognizes the
fact when I try to read the message, and it prompts me, asking me if I
want to decrypt it.  If so, I get prompted for my passphrase and if the
message was properly encrypted with my public key, I can then read it.

However, today I received an encrypted message, and Gnus didn't
recognize it as being something to decrypt.

The message arrived as a single-part multipart/mixed message, with both
the encrypted message and the user's public key that part.

If I copy that part to a separate file and run `pgg-decrypt' on it, I
get prompted for my passphrase, and it decrypts with no trouble.  So I
know that the encryption block itself is OK.

Here's the structure of the information inside of that single part
of the multipart/mixed message:

  -----BEGIN PGP MESSAGE-----
  Version: MailVault 2.2 from MailVault Corporation  http://www.mailvault.com

  ... base 64 stuff ...

  -----END PGP MESSAGE-----


  PGP Public Key for Sender <sender@sendingdomain.tld>:

  -----BEGIN PGP PUBLIC KEY BLOCK-----
  Version: MailVault 2.2 from MailVault Corporation http://www.mailvault.com

  ... more base 64 stuff ...

  -----END PGP PUBLIC KEY BLOCK----

Could it be that Gnus doesn't recognize this block because it's within a
part of a multipart/mixed message?  Or perhaps could the extra public
key block be confusing things?

Whatever the case, is there a way to set up Gnus so that it recognizes
the encrypted message within the message part and then runs me through
the standard decryption dialog?

Thanks in advance.

-- 
 Lloyd Zusman
 ljz@asfast.com