Simple definition
A command to convert an initially unencrypted connection into a TLS-protected session.
Technical definition
STARTTLS is used by several protocols, including SMTP, to negotiate TLS after the connection is established.
What is it used for ?
Encrypt exchanges between clients and servers or between servers where configuration permits.
Practical example
A customer SMTP can connect to port 587 and then negotiate STARTTLS before authentication.
Common issues
- Server not offering STARTTLS
- Invalid certificate
- Client configured with wrong encryption mode
Related terms
SMTP · SSL/TLS certificate · Network port
Key takeaway: This entry explains the general operation of the term. Exact settings may vary depending on software, vendors and environments.