SMTP Port 587: A Guide to Checking and Troubleshooting

SMTP port 587 helps with email delivery optimization. Unlike traditional email submissions through port 25 or 465, port 587 establishes more secure and authenticated connections between a mail client and server. However, port 587 is not recognized as the default SMTP port by the Internet Assigned Numbers Authority (IANA), an organization responsible for managing the internet addressing scheme. This can lead to email server connectivity issues, resulting in failed delivery attempts.

In this article, we will guide you through the process of checking if port 587 is open. In cases where the port is obstructed, we’ll share several troubleshooting techniques and proper mail server configurations to resolve the issue.

Understanding SMTP Port 587

SMTP, or Simple Mail Transfer Protocol, is the foundation of email communication. Its function is for sending and receiving emails, enabling messages to travel across networks from one mail server to another. Port 587 plays a pivotal role in this process. While older port options support SMTP-related data transmission, port 587 ensures more robust security of outgoing emails.

Other port alternatives include ports 25 and 465. Port 25 doesn’t require authentication and is the default message relay port. On the other hand, port 465 was originally registered for SMTPS (SMTP over SSL). SMTP relaying or message relay involves transferring email messages from one mail server to another. The SMTP relay mechanism enables email communication across domains and servers. Port 465 supports SSL encryption. However, SMTPS over port 465 has been replaced by the more flexible and secure STARTTLS method, commonly used with port 587. Despite its deprecation, some ISPs and hosting service providers still support port 465 for SMTP submission.

Here are two port 587 roles that set it apart from other ports:

Standard Port for Secure Outgoing Emails
Enhanced Spam Prevention and Reliable Delivery

How to Check if Port 587 Is Open

Verifying whether port 587 is open is crucial to prevent email communication issues. However, due to ISP port restrictions, there is a chance you might encounter blocked email ports. If your preferred port is blocked, here are several common error messages that you might encounter:

Closed SMTP connect() failed.
Timeout::Error (execution expired)
Mailer Error: SMTP connect() failed.
Connection unexpectedly closed: timed out
S: SMTP ERROR: QUIT command failed: Connection: closed
2023–09–8 17:13:00 SMTP ERROR: Failed to connect to server: Permission denied (13)

There are two ways you can conduct a port status check, which we cover below:

1. Use Command Prompt/Terminal

Command Prompt on Windows and Terminal on macOS and Linux are command-line interfaces enabling users to interact with their computer’s operating system using text-based commands. Here’s how to access Command Prompt on Windows:

Press Win+R.
Type cmd in the window.
Click OK or press Enter.
You’ll arrive on Windows’ Command Prompt interface.

Here’s the guide for macOS users:

Press F4 to open the Launchpad.
In the search field, type Terminal, and press Enter.
The Terminal app will open.

For Linux users, utilize the Ctrl+Alt+T keyboard shortcut to access the Linux Terminal.

Once you successfully access your device’s command-line interface, run the telnet command in the Command Prompt or Terminal window to check if port 587 is open:

Type telnet your-email-server.com 587, and ensure to replace your-email-server.com with your actual email server’s remote host. Hostinger’s email server’s hostname is smtp.hostinger.com.
Press Enter. If the port is open, you’ll see a 220 message. On the other hand, you’ll encounter a connection refused SMTP error message if the port is closed.

2. Use Online Port Checking Tools

Aside from using the telnet command, you can utilize online port checker tools to verify port connectivity. Here’s how to use CanYouSeeMe.org to check if port 587 is open:

Visit the website and find the port checker input box.
Enter your IP address and 587 as the port number.
Click Check Port or press Enter to run the test.

If the port is open, you’ll receive a positive confirmation. If the port is closed, the tool will indicate a failure to establish a connection or an SMTP port timeout.

Troubleshooting Blocked SMTP Port 587

Encountering an SMTP error with port 587 blocked can be inconvenient, especially if you use internet email communication for business purposes. Follow these tips to troubleshoot email-sending issues and resolve them:

1. Check Firewall Settings

Firewalls are barriers between your computer and the internet, safeguarding your system from unauthorized access and malicious traffic. Unfortunately, firewalls can cause an SMTP error as they might block legitimate traffic, including port 587, used for email communication. For email delivery troubleshooting, you can start by examining your computer’s firewall settings.

2. Verify Router and Network Configuration

Routers and network settings are crucial in determining which ports are accessible. Incorrect configurations can lead to port 587 being blocked, affecting email delivery. As such, follow these general steps to ensure your router and network aren’t causing email communication disruptions.

3. Check for ISP Restrictions

Internet Service Providers (ISPs) monitor and regulate network traffic to maintain a secure and spam-free environment. Some ISPs might block outgoing port 587 to prevent spam and unauthorized email traffic, leading to issues with sending emails using this port.

Using Port 587 at Hostinger

The email server configuration differs from one hosting service provider to another. Some companies allow port 587, while others might block it and allow other outbound ports. Therefore, checking if your provider’s mail server supports your preferred port type is crucial.

Hostinger’s business email hosting setup uses port 465 with TLS encryption as its default SMTP settings. It also allows port 25 as a message relay port. If you use Hostinger’s email services and have encryption issues during the network port testing process, you can opt for port 587.

Conclusion

Port 587 is among the most secure email server ports, but it’s not the default SMTP port of the Internet Assigned Numbers Authority (IANA). Consequently, port 587 often introduces server connectivity and email transmission issues. To prevent those issues, run SMTP port testing to verify the port 587 connectivity.

Even when your mail server supports the 587 port, an SMTP-related data transmission error may still occur. This might be connection refused, permission denied, execution expired, or connection unexpectedly closed. Proper mail server configuration is vital to ensure successful email submissions. You can check your computer’s firewall settings for email transmission, verify your router’s port forwarding configuration, or consult your ISP for SMTP port 587 restrictions.

In this SMTP connectivity guide, we also shared tips for using port 587 at Hostinger. By following the instructions in this article and setting up the proper configuration, you can enjoy reliable email communication using Hostinger’s email server.

By Edgaras G. & Linda D.

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