This is so your server won't be sending emails from your email server, the forum will use Gmail SMTP server to send and receive emails. You NEED to signup for a Gmail Email though, thats the only way you can use their SMTP Server.
I had to do this for my home server, because my ISP blocks the SMTP outgoing port. So I setup my IP.Board to use google's SMTP server. And it works. After you set it up, you can use your IP.Board to send you a test email, just to see if its working.
If you need any more help configuring your Email via IP.Board using GMAIL, let me know and I will help you the best way I can.
thetechgenius's post in User Validation Mail? was marked as the answer