SOLVED Frequent mail bounces / "Message delivery failure notice"

[subven]

Lately I got a lot of reports from my users about bouncing mails. We do not send Newsletters/Mass mails or something similar. Most of them are from Outlook.com and some from web.de and arcor.com. The reason is always Error 550 5.7.1 Reject for policy reason.

Our mailserver was never blacklisted and runs perfectly fine but the error reports say something like:

Please contact your Internet service provider since part of their network is on our block list (S3150).

Is it really because the network of my server provider (Netcup) is kinda blacklisted? I've been thinking since DKIM etc it's a bit safer....or is it really the price you pay if you host your own email server? The message content is plain text, no attachments and sometimes some URL's and telephone numbers...normal content for a mail. I can't help myself and the only solutions seems to use an external SMTP provider. I don't think it's the fault of Cloudron/Haraka but I would still like to consider all advices and solutions.

[murgero]

@subven said in Frequent mail bounces / "Message delivery failure notice":

550 5.7.1 Reject for policy reason

Have you checked if you are on any blacklists? https://mxtoolbox.com will be helpful to check a good chunk of them (almost 100!)

[nebulon]

Sometimes if a fresh VPS is created, it gets a recycled IP from a previous VPS which was for some reason blacklisted at a provider. This is not too uncommon, however contacting that provider about this and get your IP off the blacklist is mostly a one-time thing and in our experience takes only about a day. In this specific case you should probably also contact netcup about this issue and maybe they can reassign a different IP from a different block to your server to mitigate the issue.

[subven]

@murgero said in Frequent mail bounces / "Message delivery failure notice":

@subven said in Frequent mail bounces / "Message delivery failure notice":

550 5.7.1 Reject for policy reason

Have you checked if you are on any blacklists? https://mxtoolbox.com will be helpful to check a good chunk of them (almost 100!)

Yes I regularly check against an DNSBL. Additionally, Cloudron has it's own blacklist check integrated.

@nebulon It's a Root with we rented half year ago. I delisted my domain multiple times so this does not work for us. You think it's only IP/Network related? I was thinking about entire network address ranges at netcup having bad reputation

I requested access to microsofts SNDS to check the reputation of my IP/domain. So far no good solution in sight...

[subven]

Seems to be Microsofts fault. They don't ban single IP's but whole IP networks. The forum of my server provider is filled up with complaints about blocked mails. Since there is nothing TODO and cloudron works fine, I'll mark this thread as resolved.

[murgero]

@subven Have you read https://docs.microsoft.com/en-us/office365/securitycompliance/use-the-delist-portal-to-remove-yourself-from-the-office-365-blocked-senders-lis ?

You should be able to get your specific IP delisted.