Credit Squeeze?
Granted. But that's quite different, and not everyone has hit the same issues.
It tends to be that the more mass emails get sent out the more deliberability issues increase. So if this individual has been doing more of then it would be expected to hit more problems.
People starting out on this path like mailinabox, iredmail, and ISPmail. The last one walks you through the process, doesn't do it all for you. First two mostly just do it all for you.
I read this article via Google Translate, but it didn't seem to be saying that it was impossible to run your own email server successfully.
I don't agree with the conclusions. I have successfully run my own self-hosted email server since the Snowden revelations with no deliberability problems to big players.
The ISPmail howtos on WorkAround.org are a good starting point. www.iredmail.org well in a pinch. You can host your own email server at home/work on your own hardware on a static IP address, or use a VPN tunnel to a cloud VPS for their static IP address. This provides the most security.
Or else you can run it in the cloud if convenience wins.
Either way, it's not impossible. It's achievable. And it brings some significant protections, technical and legal.