Microsoft doesn't make an AV client.
Nortons? McAfee? AVG? Any of those ring a bell?
Anyway, if it's not doing it now, probably no harm. Just remember that yes there can be some false positives. You can never get AV to stop 100% of the harm whilst allowing 100% of the legit material. You balance between stopping too much legit stuff or letting in too much harm. Obviously the preference is to stop more legit stuff than let in ANY harm. :)
So sometimes legit things get flagged as problems.
Basically, if you know what you're looking at came from a reputable source, you're probably fine. Sparkpeople.com is a reputable source. But their domain look and feel and the source of the email can be forged by someone else. So be vigilant. :)
Deb, in New Zealand