Cloudron Forum

Hi, first time cloudron user here.

Cloudron version: 9.0.10
Ubuntu version: Ubuntu 24.04.3 LTS Linux 6.8.0-87-generic
Vendor: Hetzner VPS

Sometimes I am getting an error that my IP4 is blacklisted on spamhaus. But checking with spamhaus does not confirm my IP is blacklisted. It seems to be the "open resolver" issue.

Some emails sent to me are not delivered but returned with this error message:

Client host [**.**.***.***] blocked using
    zen.spamhaus.org; Error: open resolver;

I read somewhere that this could be related to the Hetzner public DNS. But I do not know how to resolve this.

Spamhaus mentions steps to solve the issue by signing up to their Spamhaus DQS and making relevant changes to the mail server configuration.
It is not clear to me which steps I have to take in regards to the Cloudron setup.

Can someone help me solve this issue? I am not very technical but do have SSH access to my server.

Hi @james

• IPv6 is enabled and configured correctly
• PTR records are also correctly set

@joseph Hi, sorry for the delay in my response. I checked my server according to the examples you gave and got the same results. So that seems to be correct.

What I gathered from this whole conversation (and my subsequent online searches) is that IPv6 is a bit of a problem for email. I guess we have to wait until some conventions are created/adopted.

@girish Thank you!
The initial error seemed indeed to be related to an IPv6 address.

Thanks everyone for helping and answering all my questions.