Attached file garbling with TNEF (winmail.dat)

I receive an email sent by outlook, an attached file’s filename garbled, sometimes.

the filename is written in Japanese.
All filename is written in Japanese garbled in this case.

I am not sure about the exact date, but it was no problems before.
The problem occurs since a month or two ago.

It is not from a specific PC but another PC as long as Outlook.
garbled attachment file comes with message.rtf. so I guess the mail sent by Rich text type. I asked the sender to check the option settings of Outlook he uses and the settings are “send by HTML type” not rich text.

I searched how to fix this problem but I couldn’t find any way to solve it.
It may have a relation with TNEF, or maybe not.

I use my email account with IMAP4 on eMclient.
I don’t know if I use POP3.

Please find out what’s going on and fix the problem.