SMTP Port 587: Overview and Comparison
Email still runs a huge part of business communication, and behind every message there is a set of protocols and ports that quietly move data across the internet. One of the most important of these is SMTP port 587. If you have ever configured an email client, website contact form, or application that sends notifications, you have likely seen this port number. It plays a central role in secure email submission and helps reduce spam and abuse while keeping legitimate messages flowing. Understanding why port 587 exists and how it compares with other SMTP ports can save time, prevent delivery problems, and improve overall email security.
Meaning
Port 587 is the standard network port used for SMTP email submission. SMTP stands for Simple Mail Transfer Protocol, the system that sends email from a client to a mail server and between mail servers. Port 587 is specifically intended for message submission by authenticated users, such as when you send an email from a mail app or a web application. It supports encryption and user authentication, which makes it safer and more reliable than older default SMTP ports.
Key details
- Designed for submission - Port 587 is meant for clients sending outgoing mail through a mail server.
- Supports authentication - Users must log in with a username and password or other credentials.
- Encryption with STARTTLS - Connections usually begin unencrypted and then upgrade to an encrypted channel.
- Reduces spam abuse - Authentication helps prevent open relay misuse.
- Widely recommended - Most email providers suggest port 587 for outgoing mail setup.
Usage
Port 587 is commonly used in email clients such as Outlook, Thunderbird, and mobile mail apps. When you configure an account, the outgoing server often requires the server address, port 587, and authentication details. Web servers and applications also use port 587 to send transactional emails like password resets, alerts, and confirmations. The typical process involves the client connecting to the server, initiating encryption using STARTTLS, authenticating, and then submitting the email message for delivery. The mail server then handles routing the message to the recipient’s server.
Common issues and troubleshooting
- Authentication errors - Incorrect username, password, or disabled SMTP auth can block sending.
- Encryption problems - If STARTTLS is not enabled or mismatched, connections may fail.
- Firewall blocks - Some networks restrict outbound SMTP traffic, including port 587.
- Wrong server name - Using the incoming mail server address instead of the SMTP server can cause errors.
- Certificate warnings - Expired or mismatched SSL certificates may trigger client alerts.
Checking account settings, verifying credentials, and ensuring encryption is enabled usually resolves most port 587 issues.
Port 587 vs. Port 25
Port 25 is the original SMTP port used mainly for server to server email transfer. Over time, it became heavily abused for spam, so many internet providers block port 25 for residential users. Port 587 was introduced to separate user message submission from server relay traffic. It requires authentication and supports modern security practices. For sending email from clients or applications, port 587 is the preferred and more reliable choice.
Port 587 vs. Port 465
Port 465 is associated with SMTP over SSL, where encryption starts immediately when the connection is established. Although it was once unofficial, it has seen renewed support in many services. The main difference is how encryption is handled. Port 587 typically uses STARTTLS to upgrade an existing connection to encrypted, while port 465 uses implicit SSL from the beginning. Both can be secure, but port 587 remains the standard recommendation for message submission in many environments.
FAQs
