feat(transport-smtp): Add a debug log for name resolution

src/transport/smtp/client/mod.rs

@@ -110,6 +110,8 @@ impl<S: Connector + Write + Read + Debug + Clone> Client<S> {
             Some(addr) => addr,
             None => return_err!("Could not resolve hostname", self),
         };
+        
+        debug!("connecting to {}", server_addr);
 
         // Try to connect
         self.set_stream(try!(Connector::connect(&server_addr, ssl_context)));