@alexm said in Spamhouse blacklist:
I am kind of struggle to understand is it the problem of OVH or the way Cloudron uses this Spamhous open relays?
VPS providers have a block of IP addresses and they cycle these IP addresses across their customers as VMs keep getting created and destroyed. This means that your IP was used by someone else previously and maybe they sent a lot of spam (an unfortunately common situation). When this happens, spam watchlists like SpamHaus place the IP address in their email blocklist . In some cases, people will wholesale block the entire VPS provider IP address range since the VPS provider is not responding to spam appropriately. There is a lot of unknowns here since all this handling is not "transparent" - an email receiver can use all sorts of blocklist providers and unknown criteria to determine if your email is "spam" or not. They might even block emails by domain name etc.
Your best bet for reliable email is to sign up and use a relay - https://docs.cloudron.io/email/#relay-outbound-mails . If you don't want to use a relay, you have to be "patient" to give your IP and domain a good reputation . You have to also get your IP/domain whitelisted from the various email block list providers. Most of the email blocklist providers have an online form that you can fill up to prove your reputation.