diff --git a/lettre/src/smtp/extension.rs b/lettre/src/smtp/extension.rs
index 937115c..88ba165 100644
--- a/lettre/src/smtp/extension.rs
+++ b/lettre/src/smtp/extension.rs
@@ -38,7 +38,7 @@ impl ClientId {
 }
 
 /// Supported ESMTP keywords
-#[derive(PartialEq, Eq, Hash, Clone, Debug)]
+#[derive(PartialEq, Eq, Hash, Copy, Clone, Debug)]
 pub enum Extension {
     /// 8BITMIME keyword
     ///
@@ -144,8 +144,8 @@ impl ServerInfo {
     }
 
     /// Checks if the server supports an ESMTP feature
-    pub fn supports_feature(&self, keyword: &Extension) -> bool {
-        self.features.contains(keyword)
+    pub fn supports_feature(&self, keyword: Extension) -> bool {
+        self.features.contains(&keyword)
     }
 
     /// Checks if the server supports an ESMTP feature
@@ -245,8 +245,8 @@ mod test {
 
         assert_eq!(ServerInfo::from_response(&response).unwrap(), server_info);
 
-        assert!(server_info.supports_feature(&Extension::EightBitMime));
-        assert!(!server_info.supports_feature(&Extension::StartTls));
+        assert!(server_info.supports_feature(Extension::EightBitMime));
+        assert!(!server_info.supports_feature(Extension::StartTls));
         assert!(!server_info.supports_auth_mechanism(Mechanism::CramMd5));
 
         let response2 = Response::new(
@@ -279,9 +279,9 @@ mod test {
 
         assert_eq!(ServerInfo::from_response(&response2).unwrap(), server_info2);
 
-        assert!(server_info2.supports_feature(&Extension::EightBitMime));
+        assert!(server_info2.supports_feature(Extension::EightBitMime));
         assert!(server_info2.supports_auth_mechanism(Mechanism::Plain));
         assert!(server_info2.supports_auth_mechanism(Mechanism::CramMd5));
-        assert!(!server_info2.supports_feature(&Extension::StartTls));
+        assert!(!server_info2.supports_feature(Extension::StartTls));
     }
 }
diff --git a/lettre/src/smtp/mod.rs b/lettre/src/smtp/mod.rs
index 293d788..5bee0d9 100644
--- a/lettre/src/smtp/mod.rs
+++ b/lettre/src/smtp/mod.rs
@@ -424,7 +424,7 @@ impl EmailTransport<SmtpResult> for SmtpTransport {
             match (
                 &self.client_info.security_level,
                 self.server_info.as_ref().unwrap().supports_feature(
-                    &Extension::StartTls,
+                    Extension::StartTls,
                 ),
             ) {
                 (&SecurityLevel::AlwaysEncrypt, false) => {
@@ -490,10 +490,10 @@ impl EmailTransport<SmtpResult> for SmtpTransport {
         // Mail
         let mail_options = match (
             self.server_info.as_ref().unwrap().supports_feature(
-                &Extension::EightBitMime,
+                Extension::EightBitMime,
             ),
             self.server_info.as_ref().unwrap().supports_feature(
-                &Extension::SmtpUtfEight,
+                Extension::SmtpUtfEight,
             ),
         ) {
             (true, true) => Some("BODY=8BITMIME SMTPUTF8"),