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Mails from Exchange Online: 450 4.4.316 Connection refused

Hello,

we have a problem with the following configuration:

The MX record of the domain points to our Sophos UTM. On this the Mail Protection is active and does the spam filter. Then the mails are forwarded to the Exchange Online host xxxxxx.mail.protection.outlook.com.
This works quite well so far. However, we do not receive any mails that come from other Exchange Online Tenants.

These senders receive the following error message:

2/28/2023 9:24:58 AM - Server at xyz.PROD.OUTLOOK.COM returned '550 5.4.316 Message expired, connection refused(Socket error code 10061)'
2/28/2023 9:20:16 AM - Server at mydomain.de (mySophosIP) returned '450 4.4.316 Connection refused [Message=Socket error code 10061] [LastAttemptedServerName=myDomain.de] [LastAttemptedIP=mySophosIP:25] [SmtpSecurity=-2;-2] [xyz.prod.protection.outlook.com 2023-02-28T09:20:17.672Z 08DB1932D1917656](Socket error code 10061)'

It looks in the error message as if Exchange Online tries to deliver the mail to my UTM, but is rejected there. But why don't I see this in the logs?

I can't find anything about this in MailManager or in the SMTP proxy logs. Is there any other place I would have to look?

Does anyone use this the same way or does anyone have an idea where the problem might be?

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0 AmTi over 1 year ago

Typically, this error means Microsoft 365 encountered a connection error when it tried to connect to the destination email server. A likely cause for this error is your firewall is blocking connections from Microsoft 365 IP addresses. Or, this error might be by design if you've completely migrated your on-premises email system to Microsoft 365 and shut down your on-premises email environment.

Please check https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/connectors-mail-flow-intelligence?view=o365-worldwide at "How do I fix error code 450 4.4.316?"
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0 AmTi over 1 year ago

Typically, this error means Microsoft 365 encountered a connection error when it tried to connect to the destination email server. A likely cause for this error is your firewall is blocking connections from Microsoft 365 IP addresses. Or, this error might be by design if you've completely migrated your on-premises email system to Microsoft 365 and shut down your on-premises email environment.

Please check https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/connectors-mail-flow-intelligence?view=o365-worldwide at "How do I fix error code 450 4.4.316?"
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