The return receipts code currently uses the default charset (or the charset of the particular Inbox folder) to determine the charset of the "From" address. However, unlike the composition of email, we don't currently check the charset of the from address and see if it is suitable. We should probably make these the same. (The current workaround, is to set you default charset, or the charset of the folder where you receive email, to something that supports the characters in from address).
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