Glossary

SSL Certificate

SSL Certificate

An SSL certificate (Secure Sockets Layer) is a digital certificate that encrypts data in transit between a client (like a browser or email app) and a server. It’s part of how HTTPS works on websites – but it’s also critical in email. 

In email, SSL (or more commonly its successor, TLS) protects data as it moves between mail clients and servers, or between servers themselvs, helping prevent eavesdropping or tampering. 

You’ll encounter SSL/TLS in places like: 

  • SMTP over SSL/TLS for securely sending messages 
  • IMAP/POP over SSL/TLS for securely retrieving email 
  • API requests to ESPs  encrypted via HTTPS 

Fun fact: SSL as a protocol is deprecated. What we call an “SSL certificate” today actually enables TLS encryption – but the old name stuck around, like “cc’ing” someone when there’s no carbon copy involved. 

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