What SMTP Ports Are Used for Email?
Understanding SMTP ports and which to use for email sending
Table of Contents
SMTP Ports for Email
SMTP (Simple Mail Transfer Protocol) uses specific network ports for email communication. Different ports serve different purposes and support different security and authentication methods.
The three main SMTP ports are 25, 587, and 465. Each port has specific characteristics and use cases. Understanding these ports helps configure email clients and servers correctly for reliable email delivery.
Test which ports your SMTP server supports using our SMTP server test tool to verify configuration and accessibility.
Port 25 (Standard SMTP)
Purpose
Port 25 is the original SMTP port, designed for server-to-server email relay. It's used for transferring emails between mail servers.
Characteristics
- Standard SMTP port for server-to-server communication
- Often blocked by ISPs to prevent spam
- May not require authentication for relay
- Typically used by mail servers, not email clients
Limitations
Many ISPs block port 25 to prevent spam, making it unsuitable for email clients. Port 25 is primarily used for server-to-server relay, not client submission.
When to Use
Use port 25 for server-to-server email relay, not for email client submission. Most email clients should use port 587 or 465 instead.
Port 587 (Submission)
Purpose
Port 587 is the standard port for email submission from clients. It's designed for authenticated email sending and supports STARTTLS encryption.
Characteristics
- Standard port for email client submission
- Requires authentication (SMTP AUTH)
- Supports STARTTLS for encryption
- Generally not blocked by ISPs
- Recommended for most email clients
Security
Port 587 uses STARTTLS to upgrade plain connections to encrypted TLS connections. This provides security while maintaining compatibility.
When to Use
Use port 587 for email client submission. It's the recommended port for most email clients and applications that send emails.
Port 465 (SMTPS)
Purpose
Port 465 uses SSL/TLS encryption from the start (implicit TLS). It was originally assigned for SMTPS (SMTP over SSL).
Characteristics
- Uses implicit SSL/TLS encryption
- Encryption starts immediately upon connection
- Still widely supported
- Alternative to port 587 with STARTTLS
Security
Port 465 provides SSL/TLS encryption from the beginning of the connection, ensuring all communication is encrypted.
When to Use
Use port 465 if your email provider requires it or if you prefer implicit TLS. Port 587 with STARTTLS is generally preferred, but port 465 is still widely supported.
Which Port to Use
For Email Clients
Use port 587 for email client submission. It's the standard, recommended port that supports authentication and STARTTLS encryption.
For Server-to-Server
Use port 25 for server-to-server email relay, though it may be blocked by some ISPs.
Alternative Options
Use port 465 if your email provider requires implicit SSL/TLS or if port 587 is not available.
Testing Ports
Test which ports are accessible and properly configured using our SMTP server test tool. Verify port accessibility, authentication, and encryption support.
Configuration Tips
- Check your email provider's documentation for recommended ports
- Test port accessibility from your network
- Verify authentication and encryption requirements
- Use port 587 as the default for email clients
- Test configuration before sending emails
