I’ve solved (?) it!! If you notice from my screenshots, I have the Windows colour scheme set to silver rather than the default blue (Display Properties). I switched it back to Blue - and…no more blurred text on the Avast Delete message in Outlook! Bizarre!! So, hopefully you can now reproduce this by switching your colour scheme to Silver in XP…

However, this is clearly a small bug of some sort - it happens with all skins, and…changing my colour scheme in Windows shouldn’t prevent an application from displaying it’s messages correctly. A fix would be nice, but in the meantime…I’ll live with Blue!!