{"id":732,"date":"2019-10-28T14:37:43","date_gmt":"2019-10-28T14:37:43","guid":{"rendered":"http:\/\/blog.hostinger.io\/hostinger-tutorials\/uncategorized\/how-to-check-if-smtp-port-587-is-not-blocked\/"},"modified":"2026-06-21T08:47:20","modified_gmt":"2026-06-21T08:47:20","slug":"smtp-port-587","status":"publish","type":"post","link":"\/ng\/tutorials\/smtp-port-587\/","title":{"rendered":"How to check if SMTP port 587 is open"},"content":{"rendered":"

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.<\/p>

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.<\/p>

Such blockages can affect individual users and organizations relying on internet email communication for various purposes. Consequently, they can hinder business operations, such as project management and customer retention.<\/p>

This article 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.<\/p>

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Understanding SMTP Port 587<\/h2>

SMTP, or Simple Mail Transfer Protocol<\/a>, 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.<\/p>

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.<\/p>

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\n SMTP Relay and SMTPS <\/p>\n <\/div>\n

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).
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\nSMTP 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.
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\nPort 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.<\/p>\n <\/div>\n \n\n\n\n<\/p>

Here are two port 587 roles that set it apart from other ports:<\/p>

Standard Port for Secure Outgoing Emails<\/strong><\/p>

Port 587 is designated for secure mail submissions to an email server.<\/p>

Unlike the more traditional message submission ports, port 587 incorporates advanced encryption mechanisms to safeguard sensitive data during mail submissions or transmissions.<\/p>

It was introduced as an alternative to port 465 and to ensure the new security policy goes well with the traditional relay traffic over port 25.<\/p>

Therefore, it is often referred to as the standard submission port.<\/p>

Port 587 utilizes the opportunistic Transport Layer Security (TLS) encryption through the STARTTLS command.<\/p>

Opportunistic TLS, or STARTTLS, provides an added layer of protection by encrypting the communication channel even when the email transmission initially begins in plain text.<\/p>

So, when an email client connects to an SMTP server using port 587, the STARTTLS command is issued, prompting the negotiation of a secure encrypted connection between the two parties.<\/p>

This encryption ensures that the data exchanged between your email client and server remains protected from potential eavesdropping or unauthorized access.<\/p>

Enhanced Spam Prevention and Reliable Delivery<\/strong><\/p>

Port 587 is a secure port for sending emails because it requires authentication. Before sending an email, the mail client must identify itself to the mail server. This helps to prevent spam and unauthorized mail submissions.<\/p>

Spammers often use automated scripts to send large numbers of emails without authentication. By requiring authentication, mail servers can prevent these scripts from being transmitted.<\/p>

Required authentication helps to ensure that only legitimate users can send emails from a particular account. This helps to prevent unauthorized users from taking over accounts and using them to send spam or phishing emails.<\/p>

Utilizing port 587 for sending messages also conforms with modern email security standards, supporting higher delivery rates.<\/p>

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\n Suggested Reading <\/p>\n <\/div>\n

Head to our article on How to Create an Email Account for Professional Use<\/a> to learn about the Hostinger email setup process.<\/p>\n <\/div>\n \n\n\n\n<\/p>

How to Check if Port 587 Is Open<\/h2>

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.<\/p>

If your preferred port is blocked, here are several common error messages that you might encounter:<\/p>

Closed SMTP connect() failed.\nTimeout::Error (execution expired)\nMailer Error: SMTP connect() failed.\nConnection unexpectedly closed: timed out\nS: SMTP ERROR: QUIT command failed: Connection: closed\n2023–09–8 17:13:00 SMTP ERROR: Failed to connect to server: Permission denied (13)<\/pre>
There are two ways you can conduct a port status check, which we cover below:<\/p>
1. Use Command Prompt\/Terminal<\/h3>
\n            \n                \n                    \n                <\/svg>\n                Important\n            <\/span>\n            
\n                Important!<\/strong> In this tip, we’ll use the telnet<\/strong> command. As a privileged command, it requires administrator rights to run. If you don’t have administrator access, your computer won’t recognize the command, and you won’t be able to run the check.\n            <\/p><\/div>\n\n\n\n<\/p>
Command Prompt<\/strong> on Windows and Terminal<\/strong> on macOS and Linux are command-line interfaces enabling users to interact with their computer’s operating system using text-based commands.<\/p>
These tools provide a direct way to execute commands, run scripts, and manage various aspects of the system without relying on a graphical user interface.<\/p>
Here’s how to access Command Prompt on Windows<\/strong>:<\/p>
1. Press Win+R<\/strong>.<\/p>
2. Type cmd<\/strong> in the window.<\/p>
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3. Click OK<\/strong> or press Enter<\/strong>.<\/p>
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4. You’ll arrive on Windows’ Command Prompt<\/strong> interface.<\/p>
\""Windows'\"<\/a><\/figure>
Here’s the guide for macOS <\/strong>users:<\/p>
1. Press F4<\/strong> to open the Launchpad<\/strong>.<\/p>
2. In the search field, type Terminal<\/strong>, and press Enter<\/strong>.<\/p>
3. The Terminal<\/strong> app will open.<\/p>
For Linux<\/strong> users, utilize the Ctrl+Alt+T<\/strong> keyboard shortcut to access the Linux Terminal<\/strong>.<\/p>
Once you successfully access your device’s command-line interface, run the telnet command<\/a> in the Command Prompt or Terminal window to check if port 587 is open:<\/p>
1. Type telnet your-email-server.com 587<\/strong>, and ensure to replace your-email-server.com<\/strong> with your actual email server’s remote host. Hostinger’s email server’s hostname is smtp.hostinger.com<\/strong>.<\/p>
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2. Press Enter<\/strong>. If the port is open, you’ll see a 220<\/strong> message.<\/p>
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On the other hand, you’ll encounter a connection refused<\/strong> SMTP error message if the port is closed.<\/p>
2. Use Online Port Checking Tools<\/h3>
Aside from using the telnet<\/strong> command, you can utilize online port checker tools to verify port connectivity. Here’s how to use CanYouSeeMe.org<\/a> to check if port 587 is open:<\/p>
1. Visit the website and find the port checker input box.<\/p>
2. Enter your IP address and 587<\/strong> as the port number.<\/p>
\""CanYouSeeMee.org's\"<\/a><\/figure>
3. Click Check Port<\/strong> or press Enter<\/strong> to run the test.<\/p>
\""CanYouSeeMee.org's\"<\/a><\/figure>
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<\/strong> or an SMTP port timeout<\/strong>.<\/p>
Troubleshooting Blocked SMTP Port 587<\/h2>
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:<\/p>
1. Check Firewall Settings<\/h3>
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\n                Important!<\/strong> You need to have administrator rights on your computer to troubleshoot blocked ports by modifying the Firewall<\/strong> settings. This is because port 587 is restricted, and you need administrator access to make changes to it.\n            <\/p><\/div>\n\n\n\n<\/p>
Firewalls are barriers between your computer and the internet, safeguarding your system from unauthorized access and malicious traffic.<\/p>
Unfortunately, firewalls can cause an SMTP error as they might block legitimate traffic, including port 587, used for email communication.<\/p>
For email delivery troubleshooting, you can start by examining your computer’s firewall settings. This process can vary based on your operating system.<\/p>
Follow this guide if you’re a Windows <\/strong>user:<\/p>
1. Open the Start<\/strong> menu. Type Windows Security<\/strong> in the search bar and click on it in the results.<\/p>
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2. Click on Firewall & network protection<\/strong>.<\/p>
\"Firewall<\/a><\/figure>
3. Scroll down and select Allow an app through firewall<\/strong>.<\/p>
\"Firewall<\/a><\/figure>
4. Find your email client or port 587 entry and ensure it’s allowed.<\/p>
\"The<\/a><\/figure>
On macOS:<\/strong><\/p>
1. Open the Apple <\/strong>menu → System Preferences<\/strong> → Security & Privacy<\/strong>.<\/p>
2. Click on the Firewall<\/strong> tab → Firewall Options<\/strong>.<\/p>
3. Look for your email client or port 587 in the Allowed Apps<\/strong> list. If it is not listed, click on the +<\/strong> button and add it.<\/p>
4. Click OK<\/strong> to save your changes.<\/p>
On Linux:<\/strong><\/p>
1. Open the Terminal <\/strong>window.<\/p>
2. Find the firewall settings command for your distribution.<\/p>