Simple Mail Transfer Protocol (SMTP) is the foundational protocol used to send and relay email messages across the internet. It defines how email clients and servers communicate, making it possible to deliver messages from a sender’s inbox to the recipient’s—accurately and efficiently.
To put it simply: SMTP is what happens behind the scenes every time you click “Send.” Whether you’re using Gmail, Outlook, or any other client, SMTP ensures that your message travels from your device to the intended destination.
SMTP operates over TCP, not UDP, which ensures reliable, ordered data delivery. It uses specific ports—25 for server-to-server communication, 587 for email submission with STARTTLS, and 465 for SMTP over SSL/TLS encryption.
Since SMTP was not designed with native security features, it has become a frequent target for attackers. SMTP vulnerabilities—like spoofing, phishing, and open relay abuse—make it essential to enforce additional layers of security when using the protocol.
Today’s secure SMTP environments often rely on:
- SMTP with TLS or SSL to encrypt messages during transmission
- SPF, DKIM, and DMARC to verify sender authenticity and prevent spoofing
- Authentication protocols to block unauthorized message submissions
However, securing email isn’t just about configuring ports or enabling encryption. You need visibility across your entire network to spot anomalies, protocol misuse, or stealthy SMTP attacks.
This is where Fidelis Network® plays a critical role. It provides deep inspection of SMTP traffic, detects policy violations, flags suspicious behavior, and offers real-time alerts—empowering security teams to respond quickly and accurately.
So, what does SMTP stand for?
It stands for Simple Mail Transfer Protocol—but in today’s threat landscape, it also stands for a communication channel you can’t afford to overlook.
