exmarketplace.com is not an official google adsense publishing partner, please be wary to give them your website sensitive details likes username and password. I think they target the website which they want to do something to get some profit by getting some stuff removed.
We have received below email from them without any link that state they are the official partner, they do not have any sources that confirm they belong to official channel.
We work in partnership with Google to recruit purely high volume, quality publishers such as yourself to the Google Ad Exchange for both AdX Display and now also Google’s AdX Native product.
AdX is the premium version of Adsense and typically delivers publishers a 25% increase to their Adsense display revenues. AdX native is typically delivering a 50% higher cpm to that of Adsense display.
In addition to these significant revenue increases, both products have high global fills across all devices, can have a floor cpm applied, custom sizes created and can be run as part of a stack.
The demand for Q2 is currently extremely strong so now is a great time to test! Please just let me know if you have any questions or indeed if you would like me to request tags and logins for a trial.
Business Development Manager