Blocked ports

Last update: May 27 2025

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 when it passes border routers at the edge of the Selectel 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 unlocked	✗	for public addresses of a dedicated server (except for addresses in pools TAS-2, ALM-1, NBO-1); of the cloud server's public subnet (except for subnets in pools TAS-2, ALM-1, NBO-1) Can be unblocked: To unblock , create an unblock request for TCP port 25	for a public dedicated subnet of a dedicated server; of the cloud server's public subnet Can be unlocked: To unlock , 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 Selectel mail service, as well as mail connections on TCP ports 587 and 465 or mail sending services:

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

For more information on configuring mail sending via SSMTP, see the instructions Configuring Mail Sending via SSMTP.

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

Create request to unblock 25 TCP-port⁠

Each application will be reviewed individually, unblocking is not guaranteed. If we approve the request, we will unblock port 25:

• for dedicated servers — from all public dedicated subnets of the account, as well as public shared IP addresses specified in the application;
• cloud servers — from all public subnets of the account. You cannot unblock a public IP address. You can see if a public IP address is shared in the control panel: in the top menu, click Products → Cloud Servers → Networks → Public IP Addresses tab.

To create an application:

1. Create a ticket requesting to unblock port 25 for the account.
2. If you need to unblock the public IP addresses of dedicated servers, specify these IP addresses in the ticket. You can view the public IP address of a dedicated server in the control panel: in the top menu, click Products → Dedicated Servers → Server page → Network tab . If the address is in the /32 subnet  — this is the public IP address that you need to specify 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.