spam settings quietly changed?

[#1]

Today I registered an account at eBid, but I did not receive their registration confirmation email.
On March 20th a genuine email sent to my account bounced back to the sender. Fortunately the sender was able to inform me via my Google Mail account.
Suspecting that these incidents were related I examined the Manage My Mail settings, only to find that Spam Filtering had quietly been turned "On". I had turned it "Off" last year because no spam filter can ever be 100% reliable, and I would rather receive spam than lose genuine email.
So I turned Spam Filtering "Off" again, as well as turning Edge Protection "Off". I have now received the eBid registration confirmation email after requesting they resend it.
God only knows what other genuine email has been dumped since Spam Filtering was turned "On".
My question is: why were my spam settings quietly changed by PlusNet?

[#2]

The change you referred to unfortunately happened inadvertently during the roll-out of the updated Manage My Mail tool on 02/04/2008. This was soon picked up in the support topic for that roll-out (Postini Feedback / Manage My Mail Improvements) and PlusNet attempted to correct user settings, alas unsuccessfully for some users.
The referenced thread gives full details of this and the problem you experienced is described under Problem 50951 Customers spam preferences changing following MMM roll-out in the first post in that thread.

[#3]

Thank you for the reply. The March 20th bounce must have been something else then.

[#4]

The March 20 bounce could have been the effect of Blatant Spam Blocking (BSB) which was still active then (even though you had PlusNet spam filtering turned off).
Using the enhanced settings provided through the updated Manage My Mail tool you've now been able to turn BSB (Edge Protection) off. That enhancement seems to be giving you the additional control you needed.