Go to the TechNet article Microsoft 365 URLs and IP address ranges.Log into the Barracuda Message Archiver as the administrator, and go to the Mail Sources > SMTP page.Note: For Microsoft 365 Germany endpoints, see the TechNet article Microsoft 365 Germany endpoints. See the TechNet article Microsoft 365 URLs and IP address ranges for further details. Microsoft 365 Common and Office Online.Skype for Business Online and Microsoft Teams.SharePoint Online and OneDrive for Business.The endpoints are grouped into four service areas: Microsoft publishes a list of IP addresses used for Microsoft 365 endpoints. Add Microsoft 365 Endpoints to the Trusted SMTP Servers List If the Barracuda Message Archiver is accessible, you have set Allow Only Trusted Hosts on the Mail Sources > SMTP page to Yes, and you are attempting to telnet from an IP address not listed in the Trusted SMTP Servers section, telnet establishes a connection and the connection is immediately closed.If the Barracuda Message Archiver is accessible and you have set Allow Only Trusted Hosts on the Mail Sources > SMTP page to No, telnet establishes a connection to the Barracuda Message Archiver:.In this case, troubleshoot your network settings: If the Barracuda Message Archiver is not accessible, either due to port 25 being blocked or incorrectly configured on the firewall, the attempt to telnet simply hangs at Trying.You can test this by attempting to telnet to the Barracuda Message Archiver on port 25. Additionally, you can optionally have a public DNS record. To journal mail directly from Microsoft 365 to your Barracuda Message Archiver, you must have a public IP address and port 25 open and NATed to the Barracuda Message Archiver.

Ensure Public Access to Port 25 on the Barracuda Message Archiver

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