How to Check Open Email Ports on Your Server
Email relies on several well-known TCP ports to send and receive messages. If any of these ports are blocked by a firewall, misconfigured, or not listening, your mail server cannot communicate with the outside world. A port scan tells you exactly which ports are open, closed, or filtered, so you can quickly pinpoint connectivity issues that prevent email from flowing.
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Use our free Port Scanner to check all common email ports on your server in seconds.
Step 1: Enter Your Domain or IP in the Port Scanner
Open the Email Armory Port Scanner and enter your mail server's domain name (e.g., mail.example.com) or IP address. The tool will probe all standard email ports and report whether each one is open, closed, or filtered. Click "Scan" to begin.
Step 2: Understand the Results
The scanner checks each port and returns one of three statuses:
- Open — A service is listening and accepting connections on this port. This is what you want for the ports your mail server uses.
- Closed — The port is reachable but no service is listening. The mail server software may not be running or is not configured to listen on that port.
- Filtered — A firewall or network device is blocking the connection entirely. The scanner cannot determine whether a service is running behind the filter.
Step 3: Check SMTP Ports (25 and 587)
SMTP (Simple Mail Transfer Protocol) uses two primary ports:
- Port 25 — Used for server-to-server email relay. Your mail server must accept connections on port 25 to receive email from other servers on the internet. If port 25 is closed, no one can deliver email to your domain.
- Port 587 — The mail submission port used by email clients (Outlook, Thunderbird, mobile apps) to send outgoing email through your server. It requires authentication and supports STARTTLS encryption. If port 587 is closed, your users cannot send mail.
Some servers also use port 465 for SMTP over implicit TLS (SMTPS). While it was briefly deprecated, it has been re-standardized and is used by many modern email clients.
Step 4: Check IMAP Ports (143 and 993)
IMAP (Internet Message Access Protocol) lets email clients synchronize messages while keeping them on the server:
- Port 143 — Standard IMAP with optional STARTTLS upgrade. If you enforce encryption, the server should upgrade the connection to TLS after the client connects.
- Port 993 — IMAP over implicit TLS (IMAPS). The connection is encrypted from the start. This is the recommended port for IMAP access and should be open on any modern mail server.
Step 5: Check POP3 Ports (110 and 995)
POP3 (Post Office Protocol version 3) downloads messages from the server to the client, typically deleting them from the server afterward:
- Port 110 — Standard POP3 in plain text. Avoid using this without encryption because credentials and message content are transmitted in the clear.
- Port 995 — POP3 over implicit TLS (POP3S). If you support POP3 at all, this is the port to use.
Unless your users specifically need POP3, consider disabling it and using IMAP exclusively. IMAP offers better multi-device synchronization and keeps messages on the server.
Step 6: Troubleshoot Closed or Filtered Ports
If any required port is closed or filtered, work through this checklist:
- Check the firewall — Review your server's firewall rules (iptables, ufw, firewalld) or cloud security group settings. Make sure the port is allowed for inbound connections.
- Verify the service is running — Confirm your mail server software (Postfix, Dovecot, Exchange) is active. Use
systemctl status postfixor equivalent to check. - Check the listening configuration — Ensure the mail server is configured to listen on the correct port and network interface (0.0.0.0 for all interfaces, not just 127.0.0.1).
- Contact your hosting provider — Many cloud providers (AWS, GCP, Azure) block port 25 by default to prevent spam. You may need to request an exemption or use a dedicated email relay service.
- Check for ISP blocking — Some residential ISPs block outbound port 25. Use port 587 for mail submission from client applications instead.
Frequently Asked Questions
What is the difference between port 25 and port 587?
Port 25 is the standard SMTP port for server-to-server email relay. Port 587 is the submission port used by email clients to send outgoing mail through an authenticated connection. Most ISPs and cloud providers block port 25 for end users to prevent spam, so client applications should always use port 587 (or 465 for implicit TLS).
Why are my email ports showing as closed?
Closed ports usually indicate a firewall rule blocking the connection, the mail server software not running, the server not listening on that port, or your hosting provider blocking the port by default. Check your server's firewall (iptables, ufw, or cloud security group), verify the mail service is running, and contact your host if they block SMTP ports.
Should I keep port 110 (POP3) open?
Port 110 transmits data in plain text and should be avoided. If you need POP3 access, use port 995 (POP3 over SSL/TLS) instead. Better yet, use IMAP on port 993 (IMAPS), which supports folder synchronization and is more suitable for users who access email from multiple devices.