I just stumbled upon the spambox of the dummy email account we use for forum notification emails, and found a handfull of people that simply where replying to forum private messages over email.
This will not work.
It clearly states in the message itself
You have just been sent a personal message by Sender on A3Wasteland Forums.
IMPORTANT: Remember, this is just a notification. Please do not reply to this email.
The message they sent you was:
... ... ...
Your replies will get nowhere and automatically deleted in 30 days. If you want to reply to a forum private message, please use the forum messaging system instead.