SMTP Port 587 vs 465: Which Port Should You Use?

SMTP Port 587 vs 465: Which Port Should You Use?

Confused about SMTP port 587 vs SMTP port 465? You're not alone. Choose the wrong port and you'll spend your afternoon troubleshooting authentication failures, bounced emails, and security vulnerabilities that could have been avoided with five minutes of reading.

Really, most developers just want their emails to send reliably and securely. The port you choose affects both, so let's cut through the port jargon and get you set up correctly.

TLDR: Use SMTP port 587

SMTP port 587 with StartTLS is your best bet. It's the current standard, widely supported, and handles both secure and non-secure connections gracefully. Port 465 works but comes with baggage. It was technically deprecated, then un-deprecated, creating confusion that persists today.

If you just need to configure your email client and move on with your life, use port 587 with StartTLS email encryption. Your emails will send, your security team won't complain, and you can focus on building features instead of debugging mail server configurations.

SMTP port 587 vs. port 465 head-to-head comparison

Different SMTP ports serve different purposes, and understanding when to use each one can save you from late-night debugging sessions.

When to use SMTP port 587

Port 587 should be your default choice. It was designed for email client submission and supports StartTLS, which means connections start unencrypted and upgrade to secure as needed. This flexibility makes it work in more environments than port 465.

Use SMTP port 587 when:

• Setting up email clients (Outlook, Thunderbird, mobile apps)

• Configuring applications to send transactional emails

• Working in corporate environments with standard firewall rules

• You want maximum compatibility across email providers

Most email service providers (including Gmail, Outlook, and Twilio SendGrid) recommend port 587 as the primary choice for message submission. It requires authentication, supports encryption, and plays nicely with modern security standards.

When to use SMTP port 465

Port 465 uses implicit TLS, meaning the connection starts encrypted from the first packet. While this sounds more secure in theory, it's actually less flexible than StartTLS and can cause compatibility issues.

Use SMTP port 465 when:

• Port 587 is blocked by your network or ISP

• Working with legacy systems that specifically require implicit TLS

• Your email provider doesn't support StartTLS on port 587 (rare)

• You're maintaining existing configurations that already work

Port 465 has a complicated history, though. It was deprecated in favor of port 587, then restored years later due to widespread usage. This back-and-forth created confusion, but the port works fine for its intended purpose.

TLS vs StartTLS breakdown

The security difference between ports comes down to how encryption is handled:

StartTLS (Port 587):

• Connection begins unencrypted

• Client and server negotiate encryption upgrade

• Falls back gracefully if TLS isn't available

• More compatible across different network configurations

Implicit TLS (Port 465):

• Connection starts encrypted immediately

• No negotiation phase

• Fails completely if TLS handshake fails

• Can cause issues with some firewalls and proxies

StartTLS is generally preferred because it's more robust. If encryption isn't available, the connection can continue unencrypted (though you probably want to catch this in testing). With implicit TLS, no encryption means no connection at all.

SMTP port configuration examples

Gmail SMTP settings

• Server: smtp.gmail.com

• Port: 587 (recommended) or 465

• Security: StartTLS (587) or SSL/TLS (465)

• Authentication: Required

Outlook SMTP settings

• Server: smtp-mail.outlook.com

• Port: 587

• Security: StartTLS

• Authentication: Required

Twilio SendGrid SMTP settings

• Server: smtp.sendgrid.net

• Port: 587 (recommended), 465, or 2525

• Security: StartTLS (587, 2525) or SSL/TLS (465)

• Authentication: API key required

What about port 25 and port 2525?

Port 25 is the original SMTP port for server-to-server communication. Don't use it for client applications. Most ISPs block it to prevent spam, and it doesn't require authentication by default.

Port 2525 is an unofficial alternative that many email service providers support when standard ports are blocked. It works exactly like port 587 but on a different number. Think of it as port 587's backup plan.

Frequently asked questions

Q: Which SMTP port is most secure?

A: Both port 587 with StartTLS and port 465 with SSL/TLS are equally secure when properly configured. The difference is in how encryption is established, not the level of security provided.

Q: Why do some guides recommend port 465 over 587?

A: Usually due to outdated information or specific compatibility requirements. Port 587 is the current standard and should be your first choice unless you have a specific reason to use port 465.

Q: Can I use port 25 for sending emails?

A: Not recommended for client applications. Port 25 is for server-to-server relay and many ISPs block it. Use port 587 or port 465 instead.

Q: What if my ISP blocks all SMTP ports?

A: Try port 2525, which many email providers support as an alternative. If that doesn't work, you may need to use your ISP's SMTP server or switch to an API-based email service.

Q: Do I need different ports for sending vs receiving?

A: Yes. These ports are only for sending (SMTP). Receiving email uses different protocols and ports: POP3 (port 110/995) or IMAP (port 143/993).

Getting started with SMTP ports

Use port 587 with StartTLS for new configurations. It's the current standard, widely supported, and designed for client email submission. Fall back to port 465 if you encounter compatibility issues, and avoid port 25 for client applications entirely.

The port you choose matters less than double-checking proper authentication and encryption are configured. A misconfigured secure port is less secure than a properly configured standard port.

Ready to start sending emails through Twilio SendGrid? Sign up for a free account and get 100 emails per day with full access to our SMTP service and delivery optimization tools.