Fix clippy warnings (#807)

Depending on the features chosen these attributes were left
unused.

src/message/header/mod.rs

@@ -323,10 +323,12 @@ impl HeaderValue {
         }
     }
 
+    #[cfg(feature = "dkim")]
     pub(crate) fn get_raw(&self) -> &str {
         &self.raw_value
     }
 
+    #[cfg(feature = "dkim")]
     pub(crate) fn get_encoded(&self) -> &str {
         &self.encoded_value
     }

src/transport/smtp/async_transport.rs

@@ -1,7 +1,8 @@
+#[cfg(feature = "pool")]
+use std::sync::Arc;
 use std::{
     fmt::{self, Debug},
     marker::PhantomData,
-    sync::Arc,
     time::Duration,
 };
 

src/transport/smtp/client/net.rs

@@ -1,8 +1,9 @@
+#[cfg(feature = "rustls-tls")]
+use std::sync::Arc;
 use std::{
     io::{self, Read, Write},
     mem,
     net::{IpAddr, Ipv4Addr, Shutdown, SocketAddr, SocketAddrV4, TcpStream, ToSocketAddrs},
-    sync::Arc,
     time::Duration,
 };
 

src/transport/smtp/client/tls.rs

@@ -100,6 +100,7 @@ pub struct TlsParameters {
     pub(crate) connector: InnerTlsParameters,
     /// The domain name which is expected in the TLS certificate from the server
     pub(super) domain: String,
+    #[cfg(feature = "boring-tls")]
     pub(super) accept_invalid_hostnames: bool,
 }
 
@@ -229,6 +230,7 @@ impl TlsParametersBuilder {
         Ok(TlsParameters {
             connector: InnerTlsParameters::NativeTls(connector),
             domain: self.domain,
+            #[cfg(feature = "boring-tls")]
             accept_invalid_hostnames: self.accept_invalid_hostnames,
         })
     }
@@ -322,6 +324,7 @@ impl TlsParametersBuilder {
         Ok(TlsParameters {
             connector: InnerTlsParameters::RustlsTls(Arc::new(tls)),
             domain: self.domain,
+            #[cfg(feature = "boring-tls")]
             accept_invalid_hostnames: self.accept_invalid_hostnames,
         })
     }