What is Port 25 and Why is it Blocked?

What is Port 25?

Port 25 is used for unencrypted email traffic. When sending email, or setting up any service that automatically sends emails. Communication is sent via Transmission Control Protocol. The most common protocol utilized by almost every mail client is SMTP, which uses port 25. Google, Apple, Microsoft, and Yahoo all utilize this method to send email. Simply, Port 25 is the default port utilized when sending mail via SMTP. Most of the web-based mail servers use at least ports 465 and/or 587, or now IMAP and POP 993, and also port 2525. 

Unencrypted email traffic that leaves our firewall to a cloud based server, can trigger the blacklisting of our IP address which in-turn will disallow all port25 (unencrypted) email traffic to be blocked by that controlling entity, and tarnish the rating of our security.  These agencies are there to protect the internet against the threat of spam bots, among other reasons.

Why is this Done?

Join strives to provide the safest and most reliable network experience possible. This is a common practice for enterprise spaces, ISP’s, and community based networks like college campuses. Blocking this port by default protects these environments from bad actors and having negative repercussions for the network as a whole. 

In cases where a device or email is compromised. A rogue can be set up to send thousands of spam emails, phishing attempts, and malware files to any address on the internet. When this happens, IP addresses and total networks can end up being blocked by anti-spam blacklists. 

When your IP is added to these blacklists, you could experience websites that prevent you from accessing their site or services entirely. Some services like Microsoft and Google can flag any mail or communications automatically as “Potential Spam” which can hurt your business or reputation fast. 

Is there a way to check if I’m on a blacklist?

There are websites that keep records of publicly known addresses with issues. One site we recommend is DNS Checker who has a full suite of lookup tools to aid in your search. 

A visual guide on finding your devices IP can be found via: https://jndgtl.co/ipcheck 

What are services that may have issues with Port 25 blocked?

• Scan to Email function on printers
• WordPress extensions
• Applications and Services that rely on SMTP relaying
• Spoofing Software
• User created domain clients

Having questions? Need an exception? Contact Join Digital!

We’re here to help and want to ensure our network is the safest it can be. If you experience any issues or have additional questions, don’t hesitate to reach out to our support team. 

Support Contact for Outages/Incidents: support@joindigital.com

Emailing our support address automatically creates a support incident for our team to own and review to better serve you quickly for a resolution. Simply reply to the same email thread in order to update all associated technicians. 

Support Knowledge Base: https://jndgtl.co/support