+
+ /* It appears to be impossible to detect that a TCP/IP connection has
+ gone away without reading from it. This means that we cannot shorten
+ the delay below if the client goes away, because we cannot discover
+ that the client has closed its end of the connection. (The connection
+ is actually in a half-closed state, waiting for the server to close its
+ end.) It would be nice to be able to detect this state, so that the
+ Exim process is not held up unnecessarily. However, it seems that we
+ can't. The poll() function does not do the right thing, and in any case
+ it is not always available.
+
+ NOTE: If ever this state of affairs changes, remember that we may be
+ dealing with stdin/stdout here, in addition to TCP/IP connections.
+ Whatever is done must work in both cases. To detected the stdin/stdout
+ case, check for smtp_in or smtp_out being NULL. */
+