Microsoft had an article up that purported to lead to an updated package, briefly, but that has been removed and there is now no official ETA for re-release.

In the meantime…

You’ll need to uninstall KB2412171.  How depends a little upon your operating system.

• Windows 7/Vista: Start > Control Panel > Uninstall a Program > View Installed Updates…find KB2412171 and remove it.
• Windows XP: Start > Control Panel > Add/Remove Programs.  Make sure “Show updates” (at the bottom) is checked.  Find KB2412171 and remove it.

After uninstalling KB2412171, if you are still having errors sending and receiving mail you may have to go to the settings for your e-mail account (Tools > Account Settings > E-mail accounts) and change the Secure Password Authentication setting.  Once you do that, service should be restored.