There's an enahancement request for this (
bug 13058) in bugzilla. Please vote for it!
You might be able to work around this by setting Java's default charset appropriately. I'm not sure how that's done, however. Perhaps setting the
LC_CTYPE UNIX environment variable, or adding
-Dfile.encoding=iso-8859-7 to tomcat's command line.
And it's always a good idea to get your correspondents to stop using broken mailers!