Club mailing address

I have a question.
My club members sometimes don't send emails using our club mailing address.
Automatic reply says "Emails with a blank subject are not supported." But they put some title in it.
Here is my question. If the title in the subject box is written in Japanese, it will be thought blank?
Should we use English in the subject box when using club mailing address?

FTH only supports UTF-8 characters. We do not support the double byte characters that are used in some languages.
If they use a double byte character in the subject, it will be cleared.

Dear Brian,
Thank you for your answer for my question.
I understand.
I will tell my club members about this.
I really appreciate it to you.
Best regards,
Lily