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EDBB does not normally require you to ask support to open a TCP or UDP port. Your application must listen on the required port, and your operating system’s firewall must allow the connection.
Outbound TCP port 25 has separate SMTP limits and abuse controls. Protective restrictions may also apply during attacks or abuse incidents. Inbound port 25 is unrestricted by the SMTP policy.

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Check that your application is listening

Find the required port and process. An application bound only to 127.0.0.1 or ::1 cannot accept direct connections from outside the VPS.

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Allow the required connection

Check the firewall used by your system: UFW, nftables, firewalld or Windows Defender Firewall. Open only the required protocol and port, and restrict administrative access to trusted source addresses where possible. For Debian or Ubuntu with UFW, follow the UFW guide. Keep the VNC console open before changing rules that could block your own access.

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Test from another computer

For a TCP service, replace the example IP and port with yours:
On Windows, use:
These tests check TCP connectivity, not whether the application works correctly. For UDP, use the application’s own client or a protocol-specific test; a TCP test cannot establish whether a UDP service is reachable. If the service works from one network but not another, check client firewalls, ISP restrictions and country reachability. For a server that is entirely unreachable, start with VPS not reachable.