What does 502 mean?

SMTP 502 indicates an unimplemented command:

What it means:

The command you sent is not supported by this server. The server recognized the command but cannot execute it.

Common causes:

SMTP extension not supported: Using features the server does not have. Disabled functionality: Feature available but turned off. Protocol mismatch: Expecting different capabilities.

Typical message examples:

"502 Command not implemented" "502 Feature not supported" "502 Unimplemented command"

Response:

Use alternative approaches that do not require the unsupported feature. Check server capabilities via EHLO response. Adjust your configuration accordingly.

502 says "I can't do that." Find another way to accomplish your goal.