Its so so...
It does not correspond to the transmission and reception of Japanese mail.
Sending e-mail encryption and digital signature can somehow verification of the electronic signature and decryption.
Because it can not verify the digital signature and decryption of the mailers on, save it separately, using the gpg command, and that can and decryption.
The e-mail transmission added with only electronic signature, the validation will fail.
Verification of the digital signature and the decryption is successful in the case of encryption and digital signature for the reception.
However, it must be turned into utf-8 the transmission code.
Send mail code for Japanese is iso-2022-jp.
That part has been removed when viewed mailers ipod standard electronic signature.
These may not be the problem of "oPenGP" all.
You use the Japanese e-mail encrypted as long as you use a standard ipod MUA of this software might be impossible.
japanese gentleman about
oPenGP, v5.0.10