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I am pretty sure that just hitting reply would send it back to the automated system that sends it out, and therefore it would not be received by the party you are replying to.........I know that is what happens if people try to repond to PMs direct from their email inbox notification

Unless the person has included their email addy you would need to come back and email them via their profile

you can always check by looking at what is in the TO field when you hit reply

I only receive PMs here, not emails and so I cant test it for you, but hopefully someone who knows for sure (Doc?) will be able to give you a finite answer