From protocol.c in the stunnel source:

static const struct { char *name; struct { PROTOCOL_PHASE type; FUNCTION func; } handlers[2]; } protocols[]={ {"proxy", {{PROTOCOL_PRE_SSL, proxy_server}, {PROTOCOL_PRE_SSL, NULL}}}, {"cifs", {{PROTOCOL_PRE_CONNECT, cifs_server}, {PROTOCOL_PRE_SSL, cifs_client}}}, {"pgsql", {{PROTOCOL_PRE_CONNECT, pgsql_server}, {PROTOCOL_PRE_SSL, pgsql_client}}}, {"smtp", {{PROTOCOL_PRE_SSL, smtp_server}, {PROTOCOL_PRE_SSL, smtp_client}}}, {"pop3", {{PROTOCOL_PRE_SSL, pop3_server}, {PROTOCOL_PRE_SSL, pop3_client}}}, {"imap", {{PROTOCOL_PRE_SSL, imap_server}, {PROTOCOL_PRE_SSL, imap_client}}}, {"nntp", {{PROTOCOL_NONE, NULL}, {PROTOCOL_PRE_SSL, nntp_client}}}, {"connect", {{PROTOCOL_PRE_CONNECT, connect_server}, {PROTOCOL_PRE_SSL, connect_client}}}, {NULL, {{PROTOCOL_NONE, NULL}, {PROTOCOL_NONE, NULL}}} };

*STARTTLS* is an extension to plain text communication protocols, which offers a way to upgrade a plain text connection to an encrypted (TLShttp://en.wikipedia.org/wiki/Transport_Layer_Securityor SSL http://en.wikipedia.org/wiki/Secure_Socket_Layer) connection instead of using a separate port for encrypted communication.

stunnel will use one port to communicate the encrypted information. That's what it is telling you. No need to initiate a separate port when STARTTLS is sent.

On Wed, Dec 5, 2012 at 1:27 PM, John A. Wallace [email protected] wrote:

**

The Service Level Options of the manual includes the following points:

*******protocol = proto*

application protocol to negotiate SSL (e.g.***** starttls* or***** stls *)

  *****protocol* option should not be used with SSL encryption on a
  separate port.

  Currently supported protocols:

*CIFS*

*Connect*

*Etc..***

However, in the listed protocols supported neither “starttls” or “stls”appears, even though they appear to be options as far as I can see from the above explanation. Am I missing something here, or should they be among those in the list, and can one use this setting:

Protocol=starttls

Also, I don’t really understand what this statement is telling me: “***** protocol* option should not be used with SSL encryption on a separate port.”

John A. Wallace

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