Hello Pascal BLANCHARD,
the error message shows that your IP address 89.90.126.210 is on a Microsoft blacklist (error code S3150). This means that Microsoft has classified the mail server or part of the network as potentially problematic.
Possible solutions:
1. Check the IP address for blacklists:
Check whether your IP is on general blacklists, e.g. via:
https://mxtoolbox.com/blacklists.aspx
2. Microsoft delisting request:
- Request removal from the blacklist:
- There you can request a review and unblocking of your IP address.
3. Check SPF, DKIM & DMARC:
- Microsoft could block your emails if the authentication mechanisms are not configured correctly.
- Check your SPF, DKIM and DMARC entries with:
https://mxtoolbox.com → “SPF Record Lookup”, “DKIM Lookup”, “DMARC Lookup”
4. Contact your internet provider:
- If you have no control over your outgoing IP address (e.g. with shared hosting or a dynamic IP), your ISP may need to help.
- If the mail server is managed by an external provider, you should contact their support.
5. Contact Microsoft support:
- If nothing helps, you can contact Microsoft support:
If you send emails for business purposes, another option would be to use Microsoft 365 or another professional mail server to avoid blacklisting problems.
If this is helpful, please accept the answer. Thank you.