How to find out more about this much traffic?

[247amdan]

Hi,

I have a customer, producing very much traffic, see this pic:
https://www.247activemedia.net/traffic.jpg

It's outgoing mail traffic. Or could that be something different?

How can I find out via which email address this traffic comes and what this email sends out?

The customers says that's not possible that he sends this much mails.

Thx
Daniel