Since Friday, no emails have been received to email addresses. I can send, but not receive. As far as I can see, the DNS records are fine.
Maybe you can help me with what the problem might be? Error says: JunkMail rejected - (…) is in an RBL: Error: open resolver;
First make sure that your MX hostname is not proxied. (Based on the error that you shared, it probably isn’t, but it’s always good to check that when investigating problems receiving email.) It sounds like you have configured your mail server to use a Spamhaus DNSbl and are using an open resolver. See this previous topic reply for more details.
That should get you what you need, but just in case you need more resources, here is a link to the relevant Community Tutorial.
You probably need to focus your efforts on the Spamhaus DNSbl error message and review both the configuration files of your mail server software as well as their log files. Troubleshooting your email server is unfortunately beyond the scope of the Cloudflare Community. Do you have a trusted advisor that has email server management skills?