The emails and PMs are different and separate. The emails you get should have 1. the email of the person who sent it and 2. their username.
If you don't want to respond through email (and thereby expose your email address) you can use "Memberlist" above to find their forum name and pm them back.
If you want to respond to an email I think the usual method of Reply in whatever program you use will reply to their email address.
I'll send you a test message with the email button and you can use Reply and see if my email address comes up.