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Blocked ports
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Blocked ports

To secure the Selectel 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 Selectel Internet network. For TCP port 25, only outgoing traffic is blocked.

UDP portsTCP portsTCP/UDP ports
Blocked ports17, 111, 427, 389, 520, 1900, 3702, 1121125 (outgoing traffic)135, 137, 138, 139, 445
Can be unblockedCan be unblocked: To unblock, create a request to unblock TCP port 25Can be unblocked: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. As an alternative, we recommend using Selectel mail service, as well as mail connections on TCP ports 587 and 465 or mail messaging services:

For details on how to configure mail sending via SSMTP, refer to Configuring Mail Sending via SSMTP.

If you need to send mail directly, and Selectel mail service or other 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 PlatformServers → 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 PanelServers and HardwareServers → 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.