secure is TLS from the first byte (993, 465). Otherwise STARTTLS is required, so a network that strips it gets no password; insecure, set only by mail setup --insecure for a local test server, allows plain text.
secure
insecure
mail setup --insecure
The server's host name.
Optional
True allows a plain-text login. Set only by mail setup --insecure.
The server's port.
True for TLS from the first byte. False means STARTTLS is required, unless insecure.
secureis TLS from the first byte (993, 465). Otherwise STARTTLS is required, so a network that strips it gets no password;insecure, set only bymail setup --insecurefor a local test server, allows plain text.