What Is SMTP Port 587, and Why Is It Used?

More than 347 billion emails are sent daily, yet a significant percentage never reach their destination due to misconfigured servers, spam filters, or blocked ports. If your emails are bouncing or failing to send, your SMTP configuration—specifically, SMTP port 587—could be the reason.

SMTP (Simple Mail Transfer Protocol) is the foundation of email communication. It transmits emails from a sender's server to a recipient's email provider. However, for emails to travel securely, they must be sent through the right SMTP port.

For many years, port 25 was used for outgoing email communication, but due to spam and abuse, most ISPs have blocked it. Today, SMTP port 587 is the industry standard for secure email submission, ensuring authentication, encryption, and proper email relay.

In this blog, we will learn about SMTP port 587, why it is preferred over other ports, and how to configure it correctly for secure and reliable email transmission.

Understanding SMTP and Its Role in Email Transmission

SMTP (Simple Mail Transfer Protocol) is the system responsible for sending emails between mail servers. Unlike POP3 and IMAP, which are used for retrieving emails, SMTP ensures that messages reach their correct destinations.

SMTP needs a port to communicate with mail servers, as a shipping port allows cargo ships to transport goods. Email cannot be delivered effectively without an open and functional SMTP port.

How SMTP Works in Email Transmission:

SMTP (Simple Mail Transfer Protocol) is responsible for delivering emails from a sender to a recipient securely and efficiently. Here’s how it works:

1. Email Submission:  When a user sends an email using a client like Gmail, Outlook, or Thunderbird, the client connects to an SMTP server via SMTP port 587 to submit the email for delivery.
2. SMTP Authentication:  The SMTP server verifies the sender’s credentials using username/password authentication and STARTTLS encryption to ensure secure transmission and prevent spam.
3. Message Transmission:  Once authenticated, the email is routed through the appropriate SMTP port (typically 587) to initiate secure communication between mail servers.
4. Server-to-Server Relay:  If the recipient uses a different email provider, the email is relayed between multiple mail servers, using MX records to determine the correct destination.
5. Delivery & Storage:  Once the recipient’s email server receives the message, it stores it until accessed by the user via IMAP or POP3.

What Are SMTP Ports and Why Do They Matter?

Different SMTP ports exist to handle various aspects of email transmission. Some are used for secure authentication, while others were previously used for relaying emails but are now restricted.

Why Port 587 Is the Best Choice

• Supports STARTTLS encryption, ensuring secure transmission.
• Requires authentication, reducing spam and email abuse.
• Recommended by Google, Microsoft, and major email providers for secure email sending.
• Less likely to be blocked by ISPs compared to port 25.

Using SMTP port 587 ensures better email security and deliverability, making it the preferred option for most email services.

Why SMTP Port 587 Is the Standard for Outgoing Emails

SMTP port 587 is the most widely used and recommended port for sending authenticated emails due to the following reasons:

1. Authentication to Prevent Spam

Unlike port 25, which allowed unauthenticated email relay, SMTP port 587 requires authentication (username and password) to prevent unauthorized access and spam abuse.

2. Supports STARTTLS Encryption for Security

Port 587 allows STARTTLS, an encryption protocol that ensures email messages are securely transmitted. If encryption is not supported, it can revert to plain text communication, making it adaptable yet secure.

3. Recommended by Leading Email Providers

Major email services like Gmail, Microsoft 365, Yahoo, and Cloudflare enforce SMTP 587 for outgoing emails.

4. Better Deliverability & Compliance

Using SMTP 587 ensures compliance with modern email security policies, reducing the chances of emails being flagged as spam.

Comparing SMTP Ports: Which One Should You Use?

When configuring an email client or server, choosing the right SMTP port is crucial for ensuring secure and reliable email delivery. Here’s how the most common SMTP ports compare:

How to Configure SMTP Port 587 for Secure Email Sending

To send emails via SMTP 587, follow these steps:

1. Open Email Client Settings (e.g., Outlook, Thunderbird, Apple Mai, Gmail).
2. Go to SMTP Settings → Locate Outgoing Mail Server (SMTP).
3. Set the SMTP Server Address:
   • Gmail SMTP 587: smtp.gmail.com
   • Outlook SMTP 587: smtp.office365.com
   • Yahoo SMTP 587: smtp.mail.yahoo.com
4. Set the SMTP Port to 587.
5. Enable STARTTLS Encryption to secure communication.
6. Enter Email Credentials (username and password).
7. Test by Sending an Email to verify the setup.

For Gmail SMTP 587, users may need to generate an App Password for authentication.

Common Issues with SMTP Port 587 and How to Fix Them

Even with proper configuration, some users experience SMTP 587 errors. Here are solutions to common issues:

1. Port 587 Blocked by ISP or Firewall

• Some ISPs and firewalls block SMTP port 587 to prevent spam.
• Solution: Contact your ISP or use port 2525 as an alternative.

2. Authentication Failures

• Occurs when the email username or password is incorrect.
• Solution: Double-check credentials and enable App Passwords if required.

3. Emails Going to Spam

• SMTP 587 alone doesn’t guarantee inbox placement.
• Solution: Set up SPF, DKIM, and DMARC records to improve deliverability.

4. TLS Encryption Not Working

• Some email clients don’t properly support STARTTLS.
• Solution: Ensure TLS settings are correctly enabled in your email client.

How SMTP Port 587 Enhances Email Security & Deliverability

Using SMTP 587 offers several advantages:

• Encrypted Communication: Emails are protected from interception.
• Spam Prevention: Authentication ensures only authorized users send emails.
• Higher Deliverability: Properly configured SMTP 587 servers have lower spam rejection rates.
• Compliance with Modern Email Standards: Ensures alignment with security policies of Google, Microsoft, and major ESPs.

For businesses using email marketing or transactional emails, proper SMTP 587 configuration is essential for reliable email delivery.

Conclusion

SMTP port 587 is the gold standard for secure and authenticated email transmission. Unlike older ports, it ensures encrypted communication, prevents unauthorized email relays, and enhances email deliverability through proper authentication. 

Whether configuring Gmail SMTP 587, setting up a business email server, or troubleshooting email-sending issues, using port 587 with STARTTLS encryption is essential for maintaining a secure, spam-free email environment. To ensure reliable email hosting with proper SMTP configuration, consider Vodien’s professional email hosting services, offering secure servers, seamless email integration, and expert support for businesses and individuals alike. 

Get started with Vodien today and experience secure, hassle-free email communication!

FAQs on SMTP Port 587

Why is SMTP port 587 preferred over port 25?

Port 25 is meant for server-to-server email relay, but ISPs block it to prevent spam. Port 587 is the standard for authenticated email submission.

Does Gmail use SMTP port 587 for sending emails?

Yes, Gmail SMTP port 587 is the recommended outgoing port, requiring authentication and STARTTLS encryption.

What is the difference between SMTP ports 465 and 587?

Port 465 was used for SMTPS (SSL encryption) but is now deprecated. The modern standard is port 587 with STARTTLS.

Can I use SMTP port 587 without authentication?

No. SMTP 587 requires authentication (username and password) to prevent spam.