not all email received

[trend-1]

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.

[james]

Hello @trend-1 and welcome to the Cloudron forum

These days many anti-spam providers are also checking for IPv6.
Please check if IPv6 is enabled and configured.
Also, can you share a screenshot of your mail status form the Cloudron Dashboard?
Did you set the PTR records correctly? See https://docs.cloudron.io/email/#ptr-record

[trend-1]

Hi @james

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

[james]

Hello @trend-1
Since you stated you are a new Cloudron user, I also assume your Cloudron is very fresh.
Meaning, also your mail servers IP reputation started from a negative value (all IPs do that, nothing to worry about).
This issue should resolve itself over some time.
Spamhaus states:

queries made via a public/open server may be blocked

Important keyword is may.

This is mostly due to the negative reputation which will get better pretty fast.
If you wish to get more details on this topic, here is the offical documentation from Spamhaus https://www.spamhaus.com/resource-center/help-for-spamhaus-projects-legacy-blocklist-users/#error-code-127-255-255-254-is-causing-problems-for-my-email-stream

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As a temporary solution you could simply remove zen.spamhaus.org from your Mail ACL in the Mail Server settings in the Cloudron Dashboard.
There is also this great post from @d19dotca about spam filtering https://forum.cloudron.io/post/105256 if you'd like to improve on that part as well.

[trend-1]

Hi @james ,

Thank you for your reply. Although I am new to Cloudron I did have other servers on the same IP. The reputation is good. Checking on mxtoolbox shows all ok's.

I switched to Cloudron because of a more easy, polished and stable platform (am happy so far ). But I do need to send and receive emails.

I will check the information in the post about spam filtering. Looks interesting.

Still I would like to now the answer, if possible, to my question about what steps to follow when signing up to Spamhaus DQS and making relevant changes to the mail server configuration. What changes would I have to make in Cloudron ?
How to go about ? Or is that a no-go from Cloudron's perspective ?