Port 587 (SMTP Submission)
TCPSMTP Message Submission — SMTP Submission listens on port 587 by default.
What is Port 587?
Port 587 is the standard port for SMTP message submission, used by email clients to send outgoing mail to their mail server. Unlike port 25 (used for server-to-server relay), port 587 is specifically designed for authenticated email submission.
SMTP on port 587 requires authentication before accepting messages, preventing unauthorized use for spam. The connection starts as plain text and is upgraded to encrypted using the STARTTLS command. RFC 6409 defines the submission protocol and mandates authentication.
Port 587 is the recommended port for configuring email clients (Outlook, Thunderbird, Apple Mail). It combines authentication with encryption to protect credentials and message content. The alternative port 465 provides implicit TLS without the STARTTLS upgrade step.
Port 587 Security
SMTP Submission on port 587 should be secured with appropriate access controls and monitoring. Ensure the service is only accessible from trusted networks by configuring firewall rules to restrict access. If the protocol supports encryption, enable TLS/SSL to protect data in transit.
Regularly update SMTP Submission to the latest version to patch known vulnerabilities. Monitor port 587 for unauthorized access attempts and implement rate limiting where possible. Follow the principle of least privilege when configuring access permissions.
How to Check Port 587
To check if port 587 is open on a remote host, use nmap: 'nmap -p 587 hostname'. For a quick TCP connection test, use: 'telnet hostname 587' or 'nc -zv hostname 587'. On Windows PowerShell, use: 'Test-NetConnection -ComputerName hostname -Port 587'.
To check if port 587 is listening on your local machine, use: 'netstat -tlnp | grep 587' on Linux, or 'ss -tlnp | grep 587'. On Windows, use: 'netstat -an | findstr 587'. For a comprehensive scan, use: 'nmap -sV -p 587 hostname' to detect the service version running on the port.
Related Ports
Frequently Asked Questions
What is port 587 used for?
Port 587 is the default port for SMTP Message Submission (SMTP Submission). It is used for smtp submission communication using the TCP protocol.
Is port 587 TCP or UDP?
Port 587 uses TCP. TCP is used because smtp submission requires reliable, ordered data delivery.
Should port 587 be open?
Port 587 should only be open if you are actively running SMTP Submission. Close unused ports to reduce your attack surface. If needed, restrict access to trusted IP addresses using firewall rules.
How do I check if port 587 is open?
Use 'nmap -p 587 hostname' to scan remotely, or 'netstat -tlnp | grep 587' to check locally on Linux. On Windows, use 'Test-NetConnection -Port 587 hostname' in PowerShell.
How do I secure port 587?
Secure port 587 by restricting access with firewall rules, using encryption (TLS/SSL) where supported, keeping SMTP Submission updated, using strong authentication, and monitoring for unauthorized access attempts.
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