Whitelisted mail address marked as [-SPAM-]

[#1]

This morning I had an email marked as [-SPAM-] from a retailer I sometimes use. I've got my Plusnet spam filtering set so that suspected spam still gets sent to my inbox but is just marked as such.
Checking my whitelist I found the domain was there OK, so I have now added the full email address, BUT, over the last week I've had several other emails from exactly the same address (all with different Subject lines) which have not been marked [-SPAM-], so I wonder if the Plusnet spam filter has a hidden setting that over-rides the whitelist after a certain number of messages over a few days. Any ideas?

[#2]

Possibly some content in that specific email which triggered the spam filter.

[#3]

I can't see anything! (It's promoting footwear fit for the Autumn and is less spammy than some of the other recent ones.)

[#4]

Ah, but you don't know what the Cloudmark spam filter regards as spam. 😀

[#5]

True!
The thing is though that I whitelisted the domain, which worked up to yesterday, yet it got marked as spam today. Had I not got it set to allow marked spam into my inbox I wouldn't know it had been sent.

Hopefully, now I've put in the full address and not just the domain name that won't happen again.

[#6]

You say you've whitelisted the domain, it may be worth checking that this latest one is coming from the same domain, and that retailer hasn't decided to change or add a subdomain to send from or something like that.  That's the only thing I can think of, sorry!

[#7]

@Mad_Moggies 

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Hopefully, now I've put in the full address and not just the domain name that won't happen again.

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That is not going to help, maybe make things worse. As @pjmarsh says if the sending address has slightly changed then your very precise whitelist entry is going to be ignored.

[#8]

Also check the Envelope-From: address (usually shown as Return-Path: in headers) hasn't changed. Many spam systems will check that rather than the From:

[#9]

Thanks (everyone),

I've now compared the full headers with the last several that didn't get marked as spam.
The ONLY difference (in the things that don't change from one email to another) is that there is an extra line, an 'X-lpas:' level, above the 'X-Cm-Score:' and 'X-Pn-Pstn:' spam level. I don't know if that being there is just because it's been identified as spam or not as I have no other emails marked as spam to compare it with! (It's unusual for me to get any emails marked as spam.)
I'll go back to my whitelist and tweak the settings so there's only one for that domain/email address as suggested.
Thanks again everyone for your suggestions.

[#10]

Further to this, I got an email from them this morning that was not marked spam, so fingers crossed it won't happen again!