Hello, I setup a mail server using a Ubuntu CyberPanel droplet, everything is properly configured. Test results are 10/10, link here: https://www.mail-tester.com/test-8egaldi6p
The following message was received from outlook:
This is the mail system at host domain.com.
I’m sorry to have to inform you that your message could not be delivered to one or more recipients. It’s attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system
firstname.lastname@example.org: host outlook-com.olc.protection.outlook.com[18.104.22.168] said: 550 5.7.1 Unfortunately, messages from [22.214.171.124] weren’t sent. Please contact your Internet service provider since part of their network is on our block list (S3140). You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. [MW2NAM12FT006.eop-nam12.prod.protection.outlook.com] (in reply to MAIL FROM command)
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What I would usually suggest in such cases, is to send an email to the following website which will generate a nice report highlighting the reasons that might be causing the problem that you are seeing:
On another note, what I could also suggest is going through the following tutorial on why you might not want to run your own email server:
Hope that helps!