https://www.queryclick.com/app/uploads/2015/10/Gmail-ads-101...
https://support.google.com/google-ads/answer/7019460?hl=en
If I saw an ad in my email client, my immediate action would be to find a new email client.
https://www.queryclick.com/app/uploads/2015/10/Gmail-ads-101...
https://support.google.com/google-ads/answer/7019460?hl=en