Hi anonymous user,
According to your error message above, looks like you have encountered issues when sending emails to your Outlook.com email account, right?
Can you successfully send emails out to other external email accounts?
Are you able to receive inbound emails properly?
11-6-2021 15:56:14 - Server at outlook.com (188.8.131.52) returned '451 4.4.397 Error communicating with target host. -> 421 4.2.1 Unable to connect -> SocketConnectionRefused: Socket error code 10061'
I did some research about this specific error, most of the related information says the 25 port is the key of this issue. So, please try to check the firewall and make sure that all ports required by Exchange are opened, especially 25. For more information, please check: Network ports required for mail flow (no Edge Transport servers).
Besides, you could also try the Microsoft Remote Connectivity Analyzer tool to check the process of your Outbound SMTP Email and Inbound SMTP Email(if necessary).
Hope this can be useful.
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