What's in it for Google? It will scan the contents of that 1 Gigabyte of messages looking for keywords in order to display advertisements relevant to your online conversations. The concept has raised privacy concerns, but is probably no more invasive than the other hosted mail services such as AOL, Hotmail, MSN, and Yahoo! that routinely scan all messages for viruses and spam. The impact for marketers will come from the contextual advertising Google plans to beam at every user based on keywords found in their mail.

Think about it. You send an email marketing message to your existing customer base of optin subscribers announcing a new product. Until now, you controlled all the marketing real estate in the message. With Gmail, you will be sharing that real estate with any competitor willing to pay for the contextual ad space.

How big a problem might this pose? It depends on the number of users G-mail can amass with this exceptional value proposition. But consider that, for B2C marketers, 45 to 60 percent of all subscribers already use one of the current top three Web-hosted email services: AOL, Yahoo and MSN/Hotmail. Also, once Gmail is out there, it may be difficult for these competitors not to follow suit. Yahoo has already responded by increasing its mailbox capacity by 100%.

The Gmail concept of contextual advertising could soon become the norm for email marketing. If it does, there will be new ground rules and best practices, all of which we will analyse and keep you informed of. Stay tuned.