What is port 587 used for?
Email submission from mail clients and apps, upgraded to TLS with STARTTLS.
Should port 587 be open?
Usually open to the internet. This port is meant to be reachable publicly on servers that offer the service. This is the port apps and email clients should use to send mail through a provider. It requires a username and password or API key.
See what is listening on port 587
# Linux
sudo ss -tlnp | grep ':587 '
# macOS
sudo lsof -nP -i TCP:587 -sTCP:LISTEN
# Windows (PowerShell)
Get-NetTCPConnection -LocalPort 587 -State ListenOpen or block port 587 in a firewall
# Ubuntu / Debian (ufw)
sudo ufw allow 587/tcp
sudo ufw deny 587/tcp
# Windows (PowerShell, as administrator)
New-NetFirewallRule -DisplayName "Port 587" -Direction Inbound -Protocol TCP -LocalPort 587 -Action AllowOn cloud servers, also open the port in the provider’s security group or network firewall. At home, a service behind a router needs a port-forwarding rule to the device’s local IP.
Test it from outside
A port can be open on the server but blocked upstream. The Port Checker connects from the internet, so it shows what the world sees. From your own machine, use nc -vz example.com 587 (macOS/Linux) or Test-NetConnection example.com -Port 587 (Windows).
Port CheckerTest whether a server accepts connections on specific ports — web (80/443), mail (25/587/993), SSH, databases or remote desktop — and see which are open, closed or filtered by a firewall.
Open the tool Frequently asked questions
What is port 587?
Email submission from mail clients and apps, upgraded to TLS with STARTTLS.
Is it safe to open port 587?
Usually open to the internet. This port is meant to be reachable publicly on servers that offer the service.
How do I check if port 587 is open?
Enter your domain or public IP in the Port Checker with port 587. It tries a TCP connection from the internet and reports open, closed or filtered.