What Is TLS?
TLS is a security protocol that encrypts data sent over the internet to protect it from interception.
When you send an email, TLS encrypts the connection between your mail server and the recipient’s server so that no one can read the message in transit.
SendLayer uses TLS to secure all email transmissions, ensuring your messages are protected from the moment they leave your application until they reach the recipient’s mailbox.
What Does TLS Stand For?
TLS stands for Transport Layer Security. It’s a cryptographic protocol designed to provide secure communication over a network.
TLS is the successor to SSL (Secure Sockets Layer) and has become the industry standard for securing internet communications, including web browsing, email, and instant messaging.
How Does TLS Work?
TLS works by creating an encrypted connection between two systems before any data is transmitted.
When your application connects to SendLayer’s SMTP server to send an email, a TLS handshake occurs. During this handshake, both systems agree on which encryption method to use and exchange encryption keys. Once the secure connection is established, your email data is encrypted and transmitted safely.
This encryption process happens automatically in the background, so you don’t need to manually encrypt your emails. The receiving server decrypts the data on the other end using the same encryption keys.
Why Is TLS Important for Email Delivery?
TLS is critical for email delivery for several reasons:
- Authentication – TLS verifies that you’re connecting to the correct mail server and not an imposter
- Better deliverability – Major email providers require TLS encryption, and emails sent without it may be rejected or marked as spam
Modern email servers expect TLS encryption by default. If your application tries to send email without TLS, you may encounter errors like Error 421-4.7.0: TLS required for RCPT domain or Error 530-5.7.0: Must issue a STARTTLS command first.
What Is STARTTLS?
STARTTLS is a command that upgrades an existing insecure connection to a secure one using TLS.
When your application connects to an SMTP server, the initial connection starts unencrypted. The STARTTLS command tells the server to switch to an encrypted TLS connection before any sensitive data (like login credentials or email content) is transmitted.
This is different from implicit TLS, where the connection is encrypted from the very beginning. STARTTLS (also called explicit TLS) is now the standard method for securing SMTP connections and typically uses port 587.
That’s it! Now you know how TLS works.
Ready to send secure emails with SendLayer? Check out these helpful resources: