From Verse mobile send encrypt mail both to one internal user, the other external user

From Verse iOS/Verse Android send one encrypt mail both to one internal user, the other is external user. The encrypt mail was not delivered successfully, and the mail has been saved in the draft folder with below message.

Traveler - Encryption Failed. Your mail with subject "XXXXX" sent from your device was not delivered. This message has been saved to your drafts folder. The failure(s) are: No public encryption key was found in the Domino directory for "User Account Address".

But from Notes client, which can pop-up below message(Refer the attachment screenshot), and it allow sender to send this mail to external with unencrypt. Customer wish the traveler device can work as Notes client to deal with this scenario.

Mail Encryption Failure

If you choose to continue sending, the following recipient(s) will receive an unencrypted copy of the message: