I notice that when I do email marketing for a specific domain, it will tank the "coverage" that adsense reports. There will be sometimes twice as many page views, as impressions. I'm thinking this is because of advanced anti-spam filters/processes checking the content of pages when a URL appears in an email, before allowing it to go to a user's inbox. That's really the only theory I have as to why this "coverage drop" happens only when I send out emails to users. But, if so, the anti-spam features aren't checking every link, every time. That would create an immense amount of false page views. It must not recheck a link on a future email for a set period of time after it checks it. In other words, maybe it will only check a link once an hour and mark it safe for that period. Not sure.
Anyone else who does email marketing see coverage drop for domains placed inside those emails for that period?
