Are you talking about the one from here or the one(s) from your forum?
If from your forum, then that is an issue that your hosting provider will have to resolve as they are either not using DKIM and SPF, or the IP for your server that they have is blacklisted, or your domain is blacklisted or your domain/ip combo does not have enough reputation to get through some of the spam checking processes at Google/Hotmail.
In all of the above cases, your hosting provider will be the one to correct it.