Unfortunately, e-mails where the Chinese characters have all been converted to question marks are beyond fixing. Too much information is lost. Persons sending the e-mail should make sure to set the e-mail encoding to a Chinese encoding such as GB, Big5, or UTF-8.
For ideas on how to prevent e-mail from being corrupted in the first place, please visit the tutorial on e-mail at www.ChineseComputing.com. Also see Sending and Receiving E-Mail in Chinese under Windows: An Overview.
An off-line version of this service is now available as part of the DimSum Chinese Tools program.
The Hindi Unicode Repair Tool offers a similar web service for Hindi.
If you came to this page directly, you may also want to visit my other Chinese tools.