Google spiders read your email text to determine relevant AdSense ads that are displayed next to the content of your Gmail messages.
But do these spiders read email attachments as well for serving targeted ads in Gmail ?
I recently had an email exchange with a Dell Support person and he sent me an invoice for some Dell Desktop as a PDF attachment. When I opened this email message, GMail showed ads for the Tamil version of AOL and they were written in Tamil language.
I scanned that email conversation again and everything was written in English. In fact there were no words or phrases in the email message that could possibly trigger an AdSense ad in Tamil language.
Then I opened the PDF attachment and it contained the address of Dell Office which is based somewhere in Tamil Nadu.
Maybe this particular line in the email attachment triggered the above ad in Gmail.
There are no privacy concerns here because no human beings are reading your Gmail email but it would still be nice to know if email attachments are taken into account by Google when determining AdSense ads.