Why are our e-mail addresses taken on the black list?

The "atecotank.com" area has all the mailles of your step disabled. Why are our e-mail addresses taken on the black list? Can you give information?

I checked the email address (omercan.akgun@atecotank.com) and the emails and it was on the bounce list due to the reason. Please see the image below:

I removed it now from the bounce list and it should be now receiving emails. To prevent this boucing related issue , please see this guide: How to Prevent Email Bouncing Related Issues

Related guides: 

Why I am not Receiving Email Notifications?

How to Remove Your Email Address from Bounce List

Regards