The Board is about getting people together and there are plenty of ways to communicate: Posting on the boards, Instant Messaging and E-mail. Of course, each method is only available to registered members.
E-mail is the best way to correspond privately with members.
As an alternative to e-mail, the board offers another private method. Instant Messaging on the boards provides instantaneous delivery to the recipient's Private Mailbox. This is useful if you see another user is online. The mail is sent and received entirely through the board, so neither you nor the recipient have to open another program or leave the board. Instant Messaging also gives both the sender and recipient greater privacy: No one's real e-mail address is revealed. Instant Messages show only the handle and name of both parties.
If a recipient isn't online, Instant Messages wait in the member's IM box until the next time s/he logs in and manually reads and/or deletes them. Hence it is a bit limited, but I'm sure does have its uses, especially if a users Email address is no longer valid.