[Exim] Decode Subject header with special characters

Hi,
its not a exim problem, but when I save some mails with a exim-filter and the
subject of a mail contained some special characters, then I need to decode
such a header to bulid a suitable filename.
e.g. Subject: =?iso-8859-1?b?5MT21vzc3w==?=

Are there some tools to decode this kind of header within a shell-script?
I looked at recode without success.
Or does somebody know how to decode it?

Regards,
G. Riess