Better change your password and about the IP address just ignore because probably its using VPN/Tor.
Yeah, I assume they're not using their own IP address. And yeah, I should change my password, though I don't think I'm in danger of whoever these people are from getting it stolen.
if you insist on changing your password, do it from your profile and open the forum from your bookmark
which effectively steal you password and account when you inputted your password
check the raw header on that email message, make sure it is originated from forum's domain name