I create rails app deployed on Heroku.
also, `exception_notification` gem enabled.

when it is on development setup ActionMailer to Gmail,
everything is fine and sends a notification from Gmail address.

but when it comes to production environment on Heroku,
I get following error when server trying to send a email.

`ActionView::Template::Error (code converter not found (UTF-8 to UTF-16))`

Could anyone tell me what's happening here?