Sounds like an encoding problem.

Which encoding is selected?

• Firefox > Web Developer > Character Encoding
• View > Character Encoding

Mail encoding suffer from some problems that doesn't exists on the web. It is possible that you are getting these messages from outdated mail software that is unable to encode subjects correctly.

If this is the case, you may get Hebrew messages correctly, but from some users get it with some encoding problems. I do remember that users whose used hotmail.com was affecting such problems, but I guess Microsoft have fixed it already. On the other hand, some popular web forums software that use email notifications sometimes doesn't encode subjects correctly, and this issue also apply to the software in use by some spammers (but I'd care less about spammers…).

Thanks