Update docs regarding exim4 and spamhaus

Author: jaapmarcus

docs/docs/server-administration/email.md

@@ -49,6 +49,14 @@ If you are unable to receive emails, make sure you have setup your DNS properly.
 
 When you are done you can check the configuration via [MXToolBox](https://mxtoolbox.com/MXLookup.aspx).
 
+## Rejected because [ip] is in black list at zen.spamhaus.org. Error open resolver: `https://www.spamhaus.org/returnc/pub/65.1.174.102`
+
+1. Go to[Spamhaus free data query account](https://www.spamhaus.com/free-trial/sign-up-for-a-free-data-query-service-account/)
+1. Fill in the form and verify your email address by via the link in the email you recive.
+1. Once logged, go to Products → DQS and you will see your Query Key and below you will see the exactly fqdn that you will need to use ZEN Spamhaus black list. Something like: `HereYourQueryKey.zen.dq.spamhaus.net`
+1. Edit /etc/exim4/dnsbl.conf and replace `zen.spamhaus.org` with `HereYourQueryKey.zen.dq.spamhaus.net`
+1. Restart exim4 with systemctl restart exim4
+
 ## How do I disable internal lookup for email
 
 If you use an SMTP relay or want to use DKIM on your web server but host email on gmail you need to disable internal lookup in Exim4.