[MlMt] addition of "***UNCHECKED***" to subject of incoming GPG-encrypted messages?

[Michael Dunston]

I apologize if I’ve missed an explanation of this somewhere obvious, 
but I’ve not been able to clarify this in the the Mailmate Help file 
or searching the email list archives.  The security status banner 
information for GPG-encrypted messages seems fairly clear:

	Successfully decrypted OpenPGP message.
	This message is also trusted to have been signed by the sender.

However the addition of “***UNCHECKED***” to the subject leads me to 
wonder what exactly was unchecked, esp. given the information provided 
by the security status banner.  Can anyone direct me to where this might 
be explained in further detail?  Thanks.