Sorry the app does not support message signing or encryption.
I would like to check why it's not able to show anything at all.
Could you please capture the issue in the app's debug log, with "raw message data" enabled, please see the link in my signature below?
With the log enabled, please open one such message, do Menu -> Diag: reload, wait for it to complete, maybe then do another one, finally send me the log file (kmansoft / gmail).
Thanks!