Lots of emails from example.com servers

So i have installed FortiMail vm for testing in my lab. And iam seeing a lot of this messages. Idont think there are something wrong with Fortimail. It seems to do its job blocking this. It can be around 1000 emails each day looking like this. Thats alot considering this lab has 3 users for testing.

The messages seems to not have any content but connect with strange from and no to:

But have anyone here experienced something like this?