Message Submission

Port 587 is designated for the SUBMISSION service, which allows email clients to submit messages to a mail server. This port is commonly used for sending emails securely using SMTP with authentication. It helps ensure that emails are sent from authenticated users, reducing the risk of spam.

What is Message Submission

Port 587 is a network port used for the SUBMISSION service, which is a part of the Simple Mail Transfer Protocol (SMTP). This port is specifically designated for email message submission from mail clients to mail servers. Unlike port 25, which is traditionally used for email relay, port 587 requires authentication, making it a more secure option for sending emails.

The SUBMISSION service on port 587 helps in ensuring that emails are sent by authenticated users, thereby reducing the chances of spam and abuse. This port supports various security mechanisms, including STARTTLS, which allows for the encryption of email communications, enhancing the overall security of email transmission.

Historically, port 25 was used for both email submission and relay, but due to its susceptibility to abuse by spammers, the Internet Engineering Task Force (IETF) recommended the use of port 587 for email submission. This change has been widely adopted by email service providers and clients to improve email security and reliability.

Message Submission runs on TCP and UDP port 587 and is official IANA port.

Security risk

If port 587 is open and the service is running without proper security measures, it can be exploited for sending spam or phishing emails. Unauthorized access to this port can lead to misuse of the email server, potentially damaging the organization's reputation and leading to data breaches.

In our UFW tutorial you can follow instructions how you can configure UFW to close port 587. Use StackChanges to monitor if the Message Submission port is closed and stays closed. StackChanges will send an alert if port 587 is open again.