It is NOT possible to respond to posts by email.
If you receive a notification of a new post or thread, the first thing it says is;
*** Do NOT reply to this message - email replies will be ignored ***
*** please visit the web site and post your response in the forum ***
This means what it says
If you wish to contact a member directly who has posted in the forum, log into the forum, go to their post and click on their username, a menu will appear showing the options to contact them.