Blocked ports

Blocked ports

To secure the Servercore infrastructure from malicious network activity, access to some TCP/UDP ports is restricted.

Inbound and outbound traffic is blocked at the moment of passing Border Routers (border routers) at the edge of the Servercore Internet network. For TCP port 25, only outgoing traffic is blocked.

	UDP ports	TCP ports	TCP/UDP ports
Blocked ports	17, 111, 427, 389, 520, 1900, 3702, 11211	25 (outgoing traffic)	135, 137, 138, 139, 445
Can be unblocked	✗	Can be unblocked: for any public addresses of the dedicated server; public subnet of a cloud server. To unblock, create a request to unblock TCP port 25	Can be unblocked: for a public dedicated subnet of a dedicated server; public subnet of the cloud server. To unblock, create a ticket

If the port does not fall under the above restrictions, check its availability on the OS side using the Nmap utility.

Mailings via port 25⁠

To prevent unauthorized mailings, TCP port 25 is blocked for outgoing connections towards public IPv4 and IPv6 addresses. Alternatively, we recommend using mail connections on TCP ports 587 and 465 or mail messaging services:

• Mailganer,
• Sendsay,
• DashaMail,
• UniSender,
• mail Google Workspace,
• mail Microsoft Office 365,
• mail Yandex 360.

If you need to send mail directly, and mail sending services are not suitable for you, you can create a request to unblock 25 TCP port.

Create a request to unblock 25 TCP port⁠

Each application will be reviewed individually, unlocking is not guaranteed. If we approve the application, we will lift the 25 port blockage:

• for dedicated servers — from all public dedicated subnets of the account, as well as public shared IP addresses specified in the application;
• for cloud servers — from all public subnets of the account. A shared IP address cannot be unblocked. To see if the public IP address is shared, you can go to Control Panel under Cloud Platform → Servers → Server Card → Ports tab. Common IP addresses are listed in the Public IP field.

To create an application:

1. Create a ticket requesting to unlock port 25 for the account.
2. If you need to unblock shared IP addresses of dedicated servers, specify these IP addresses in the ticket. To view the public IP address of a dedicated server, go to Control Panel → Servers and Hardware → Servers → Server Card → Network tab. If the address is on the /32 subnet, it is a shared IP address that must be specified in the application.
3. Wait for technical support to reply that port 25 is unblocked.
4. Check to see if mail is being sent through port 25.