Thanks for letting me know.
Please try the following if it allows you to send encrypted mail:
Open Mail.py file in lib/clenotes-directory
Find following line: newMailDocument.setSignOnSend(True)
and enter following in the new line: newMailDocument.sign()
Find following line: newMailDocument.save() and replace it with: newMailDocument.setSaveMessageOnSend(True)
Does that send encrypted mail?
For checking if encrypted mail can be sent to recipient, I try to find some way to check it. InfoCenter says this about when sending encrypted email :
To encrypt a document when mailed, this method looks for the public key of each recipient in the Domino Directory. If it cannot find a recipient's public key, the method sends an unencrypted copy of the document to that recipient. All other recipients receive an encrypted copy of the document.