Try to detect some more stranges cases

envelope.py

@@ -115,11 +115,21 @@ def check(msg, GNUPG_DIRECTORY, accept_public_key=True, beta=False):
                 yield MailTest("Standalone non-armored signature file discovered. Avoid using binary signature over SMTP (see RFC2015 #2. PGP data formats).", 2)
                 yield (part.get_payload(decode=True), lpart.get_payload(decode=True))
 
-            elif part.get_filename() is not None and (part.get_filename()[len(part.get_filename())-4:] == ".gpg" or part.get_filename()[len(part.get_filename())-4:] == ".asc") or (
-                    payload is not None and not part.is_multipart() and part.get_payload(decode=True).find(b"-----BEGIN PGP MESSAGE-----") >= 0):
+            elif payload is not None and not part.is_multipart() and part.get_payload(decode=True).find(b"-----BEGIN PGP MESSAGE-----") >= 0:
                 yield MailTest("Standalone PGP message discovered.")
                 yield part.get_payload(decode=True)
 
+            elif part.get_filename() is not None and (part.get_filename()[len(part.get_filename())-4:] == ".gpg" or part.get_filename()[len(part.get_filename())-4:] == ".asc"):
+                yield MailTest("Standalone PGP message discovered with mismatched content-type: %s. This can lead to unexpected behaviour." % part.get_content_type(), 2)
+                data = part.get_payload(decode=True)
+
+                mime = _guess_mime(data)
+                if mime == "application/octet-stream":
+                    yield MailTest("Non-armored file discovered. Avoid using binary PGP message over SMTP (see RFC2015 #2. PGP data formats).", 2)
+                    yield MailTest("Falling back to default automation as nothing helped. Be warned it'll most likely failed.", 2)
+
+                yield data
+
             lpart = part
 
 def skip(msg, gpgmail):