On Wednesday, Microsoft's (NASDAQ:MSFT) Outlook.com launched "Don't Get Scroogled by Gmail," a national campaign to educate Americans about Google's (NASDAQ:GOOGL) practice of selling targeted ads based on email contents.

According to a Microsoft-commissioned study, 70% of consumers don't know email providers "read" emails to sell ads. About 88% of people disapprove of the practice once they are informed of it, with 52% disapproving strongly. About 83% think that the practice constitutes an invasion of privacy. Outlook.com says that, unlike Gmail, it doesn't go through the content of users' emails to show ads.

As Google explains on its website, the company "scans the text of [incoming and outgoing] messages in order to filter spam and detect viruses, just as all major webmail services do. Google also uses this scanning technology to deliver targeted text ads and other related information. This is completely automated and involves no humans." So, the same technology that keeps out spam and viruses is also used to sell vacation ads regarding, say, an email conversation about a trip to Hawaii. 

According to Stefan Weitz, senior director of Online Services at Microsoft:

Emails are personal -- and people feel that reading through their emails to sell ads is out of bounds. We honor the privacy of our Outlook.com users, and we are concerned that Google violates that privacy every time an Outlook.com user exchanges messages with someone on Gmail. This campaign is as much about protecting Outlook.com users from Gmail as it is about making sure Gmail users know what Google's doing.

Outlook.com does not scan the contents of your personal email to sell ads. Outlook.com is an email service that prioritizes your own and your family's privacy. You wouldn't let the post office look inside your mail, so why would you let Google?

Fool contributor Kevin Chen has no position in any stocks mentioned. You can follow him at @TMFKang or on Google+The Motley Fool recommends Google. The Motley Fool owns shares of Google and Microsoft. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.