CPM advertising emails: What kind of scam is this?

So my company gets tons of emails like this and I usually always ignore them because every single one is the same format..some random no name marketing agency has a client with a large monthly budget.

"We have recently acquired a client interested in running a standard banner campaign on a CPM model. If possible, we would like to partner with you in running this campaign. I am currently unavailable to chat over the phone, although I would be delighted to get a campaign organized via email. Overall we would like to run the campaign for a total of 2 months with a $20K/month spend ($40K total)."

Anyone ever get emails like this? What's the deal behind it? I get these emails every few months from different people, and they are actually submitting them directly through our contact form...but they are always the same format (some client that has $20k/mo budget for a cpm campaign).