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Inbound and Outbound Port 25 (SMTP) Restrictions
SMTP (Simple Mail Transfer Protocol using TCP port 25) is the network mechanism for sending email messages. Illicit connections to computers on port 25 (SMTP) can be a security risk. This port is frequently misused to:
- Send spam, particularly spam with illegal or "malware" content
- Gain access to and take control of computers
In order to block these uses of computers on Yale’s network, connections to port 25 will be blocked by default at the network gateway. Blocking these connections at the network level protects Yale computers and the Yale network from unwanted intrusions.
This block will not affect most users. This restriction does nothing to interfere with an individual’s use of email with an account on one of the many large email servers on campus. The block will also have no effect on web-based email clients (e.g., Gmail, Hotmail).
This port 25 restriction affects only those who manage their own local, email server.
- Inbound Port 25 restrictions went into effect in May 2005.
- Outbound Port 25 restrictions will go into effect in August 2006.
- Registration of mail servers for an exemption is a simple matter of filling out a web-based form.
If you believe you need to register for this service, visit our Inbound and Outbound registration page.
Please Note:
Automatic exemptions have been made for email servers using outbound Port 25 (as determined by network scans conducted in the weeks prior to June 15, 2006). ITS staff will contact owners of systems that are sending legitimate port 25 traffic to determine whether they require a long term exemption. Please contact information.security@yale.edu if you have any questions or if you are planning to connect a new system that may require an inbound or outbound exemption.
