What is port 587 used for?

Port 587 is the standard TCP port used for SMTP Submission (STARTTLS). It is commonly used by Postfix, Exim, Mailcow, Microsoft Exchange. Modern internet standard port for email client message submission utilizing mandatory STARTTLS encryption.

How do I check if port 587 is open?

Enter your public IP or hostname into the scanner tool and click Check. A sub-second raw TCP socket handshake will be initiated from our edge server to port 587 on your target. If the 3-way handshake finishes with SYN-ACK, the port is OPEN. If an RST packet is returned, the host is reachable but the port is CLOSED. If packets time out without response, the port is FILTERED by an ISP or firewall.

Is port 587 safe to expose to the public internet?

Port 587 is generally safe to expose when running standard, patched services with strong authentication. However, always ensure your software is updated and access control policies are strictly enforced.

Why does port 587 show as closed or filtered?

If port 587 reports CLOSED or FILTERED, confirm that: 1) Your service is actively running and bound to 0.0.0.0 (not just localhost/127.0.0.1); 2) Your router has a port forwarding rule directing external port 587 to your machine's local IP; 3) Your operating system firewall (Windows Defender Firewall, ufw, or iptables) allows incoming connections on port 587.