Check if an SMTP Port Is Open with Telnet or PowerShell

Use your relay hostname from the mySMTP setup email. The examples below use the sample host relayxx.mysmtp.com.

Enable telnet

Or run this in an administrator Command Prompt:

dism /online /Enable-Feature /FeatureName:TelnetClient

Install telnet with Homebrew:

brew install telnet

sudo apt install telnet    # Debian, Ubuntu
sudo dnf install telnet    # Fedora, RHEL

Run telnet

Open a terminal or Command Prompt and connect to the port you want to test:

telnet relayxx.mysmtp.com 587

Replace 587 with 2525, 465, or 25 to test another port.

Read the result

Result	Meaning
A line starting with `220`	The port is open and the server answered
Blank screen with connection established (port 465)	The port is open. Port 465 expects TLS immediately, so no `220` greeting is shown in telnet
`Connection timed out`	The port is blocked by a firewall, router, or your ISP
`Connection refused`	Something on the path rejected the connection; check the hostname and port
`Could not resolve host` / `Unknown host`	The hostname is wrong or DNS is not working

Close the session

Type QUIT and press Enter. If the session does not respond, press Ctrl + ], then type quit.

No telnet needed. Run:

Test-NetConnection -ComputerName relayxx.mysmtp.com -Port 587

TcpTestSucceeded : True means the port is open. False means it is blocked.

Try port 2525, which is rarely blocked.
Ask your network administrator or hosting provider to allow outbound traffic to the port.
Most ISPs and cloud providers block outbound port 25. Use 587 or 2525 instead.

Use test.smtp.ai to check connectivity, TLS 1.2/1.3 negotiation, and authentication in one test.

For port and encryption details, see Supported SMTP ports and encryption. For full SMTP session tests, see Command-line test.