Microsoft NEVER send unsolicited emails anywhere. Whatever it is you have received did not come from Microsoft. I suggest you destroy it. Any cures/removal tools/patches for the blaster worm can be found in abundance on these pages.
Personally, I never open emails if I cannot identify the sender and I am expecting an email from them. Even then, my antivirus is set to check all incoming emails and ones I might even then be suspicious about I will do a manual virus check as well.
Keep your virus checker up to date.