Has someone at PN been tweaking the spam filter? A few months ago I started using spam filtering, and for a while all seemed to work very well, with only the occasional false positive. Over recent weeks, I've had to whitelist an increasing number of 'innocent parties', including The Lady magazine Superdrug Mid-Counties Co-op Crafts Beautiful magazine Cath Kidston Spotify Lidl Photobox Bowlsworld Rick Stein Ralph McTell 21 in total. The filter is on the allegedly least aggressive setting (1 on a scale of 1 - 5).
This is the problem with a ISP-hosted anti spam platform. Somebody else makes the decisions. A different user might have marked mail from, say, Superdrug, as Spam whereas you clearly don't think so. Therefore the Spam system might mark it as spam. Local spam filters are in my opinion preferable for this reason, unless you don't like having control, which is why I opt out of spam-filtering from the ISP, and would avoid an ISP where this isn't an option.