Forward first line of response for negative responses (#701)

src/transport/smtp/client/async_connection.rs

@@ -295,7 +295,10 @@ impl AsyncSmtpConnection {
                     return if response.is_positive() {
                         Ok(response)
                     } else {
-                        Err(error::code(response.code()))
+                        Err(error::code(
+                            response.code(),
+                            response.first_line().map(|s| s.to_owned()),
+                        ))
                     }
                 }
                 Err(nom::Err::Failure(e)) => {

src/transport/smtp/client/connection.rs

@@ -276,7 +276,10 @@ impl SmtpConnection {
                     return if response.is_positive() {
                         Ok(response)
                     } else {
-                        Err(error::code(response.code()))
+                        Err(error::code(
+                            response.code(),
+                            response.first_line().map(|s| s.to_owned()),
+                        ))
                     };
                 }
                 Err(nom::Err::Failure(e)) => {

src/transport/smtp/error.rs

@@ -154,10 +154,10 @@ impl StdError for Error {
     }
 }
 
-pub(crate) fn code(c: Code) -> Error {
+pub(crate) fn code(c: Code, s: Option<String>) -> Error {
     match c.severity {
-        Severity::TransientNegativeCompletion => Error::new::<Error>(Kind::Transient(c), None),
+        Severity::TransientNegativeCompletion => Error::new(Kind::Transient(c), s),
-        Severity::PermanentNegativeCompletion => Error::new::<Error>(Kind::Permanent(c), None),
+        Severity::PermanentNegativeCompletion => Error::new(Kind::Permanent(c), s),
         _ => client("Unknown error code"),
     }
 }