Yeah i've just come here to post about this so i'll add it here instead.
It's because the forum is sending without a valid from address attached.
Forum admins: If you want me to help you out then just send me a message or email to the account on.. my account
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I'm a techy bloke at a web design firm so do this day in, day out
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p.s. slob i've finally realised what your avatar is a picture of