Blocked ports

Last update: April 16 2025

Blocked ports

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

Incoming and outgoing 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	✗	You can unlock it: for public addresses of the 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) To unlock create a request to unblock TCP port 25	You can unlock it: for a public dedicated subnet of a dedicated server; of the cloud server's public subnet To unlock file a ticket

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

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 sending services:

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

Read more about setting up mail sending via SSMTP in the instruction manual Configuring mail sending via SSMTP.

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

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. To see if a public IP address is shared, go to control panels: from the top menu, press Products → Cloud servers → server page → tab Ports. Common IP addresses are listed in the column Public IP.

To create an application:

1. Create a ticket asking you to unblock port 25 for the account.
2. If you want to unblock the public 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 panels: from the top menu, press Products → Dedicated servers → server page → tab Network. If the address is on a subnet /32 — is the common IP address to 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.