diff --git a/tests/transport_file.rs b/tests/transport_file.rs
index 71e6da3..5a59049 100644
--- a/tests/transport_file.rs
+++ b/tests/transport_file.rs
@@ -1,18 +1,14 @@
 #[cfg(test)]
 #[cfg(all(feature = "file-transport", feature = "builder"))]
-mod test {
-    use lettre::{transport::file::FileTransport, Message};
+mod sync {
+    use lettre::{FileTransport, Message, Transport};
     use std::{
         env::temp_dir,
         fs::{read_to_string, remove_file},
     };
 
-    #[cfg(feature = "tokio02")]
-    use tokio02_crate as tokio;
-
     #[test]
     fn file_transport() {
-        use lettre::Transport;
         let sender = FileTransport::new(temp_dir());
         let email = Message::builder()
             .from("NoBody <nobody@domain.tld>".parse().unwrap())
@@ -48,7 +44,6 @@ mod test {
     #[test]
     #[cfg(feature = "file-transport-envelope")]
     fn file_transport_with_envelope() {
-        use lettre::Transport;
         let sender = FileTransport::with_envelope(temp_dir());
         let email = Message::builder()
             .from("NoBody <nobody@domain.tld>".parse().unwrap())
@@ -95,49 +90,21 @@ mod test {
         remove_file(eml_file).unwrap();
         remove_file(json_file).unwrap();
     }
+}
 
-    #[cfg(feature = "async-std1")]
-    #[async_std::test]
-    async fn file_transport_asyncstd1() {
-        use lettre::{AsyncFileTransport, AsyncStd1Executor, AsyncTransport};
+#[cfg(test)]
+#[cfg(all(feature = "file-transport", feature = "builder", feature = "tokio02"))]
+mod tokio_02 {
+    use lettre::{AsyncFileTransport, AsyncTransport, Message, Tokio02Executor};
+    use std::{
+        env::temp_dir,
+        fs::{read_to_string, remove_file},
+    };
 
-        let sender = AsyncFileTransport::<AsyncStd1Executor>::new(temp_dir());
-        let email = Message::builder()
-            .from("NoBody <nobody@domain.tld>".parse().unwrap())
-            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
-            .to("Hei <hei@domain.tld>".parse().unwrap())
-            .subject("Happy new year")
-            .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body(String::from("Be happy!"))
-            .unwrap();
+    use tokio02_crate as tokio;
 
-        let result = sender.send(email).await;
-        let id = result.unwrap();
-
-        let eml_file = temp_dir().join(format!("{}.eml", id));
-        let eml = read_to_string(&eml_file).unwrap();
-
-        assert_eq!(
-            eml,
-            concat!(
-                "From: NoBody <nobody@domain.tld>\r\n",
-                "Reply-To: Yuin <yuin@domain.tld>\r\n",
-                "To: Hei <hei@domain.tld>\r\n",
-                "Subject: Happy new year\r\n",
-                "Date: Tue, 15 Nov 1994 08:12:31 GMT\r\n",
-                "Content-Transfer-Encoding: 7bit\r\n",
-                "\r\n",
-                "Be happy!"
-            )
-        );
-        remove_file(eml_file).unwrap();
-    }
-
-    #[cfg(feature = "tokio02")]
     #[tokio::test]
     async fn file_transport_tokio02() {
-        use lettre::{AsyncFileTransport, AsyncTransport, Tokio02Executor};
-
         let sender = AsyncFileTransport::<Tokio02Executor>::new(temp_dir());
         let email = Message::builder()
             .from("NoBody <nobody@domain.tld>".parse().unwrap())
@@ -170,3 +137,98 @@ mod test {
         remove_file(eml_file).unwrap();
     }
 }
+
+#[cfg(test)]
+#[cfg(all(feature = "file-transport", feature = "builder", feature = "tokio1"))]
+mod tokio_1 {
+    use lettre::{AsyncFileTransport, AsyncTransport, Message, Tokio1Executor};
+    use std::{
+        env::temp_dir,
+        fs::{read_to_string, remove_file},
+    };
+
+    use tokio1_crate as tokio;
+
+    #[cfg(feature = "tokio02")]
+    #[tokio::test]
+    async fn file_transport_tokio1() {
+        let sender = AsyncFileTransport::<Tokio1Executor>::new(temp_dir());
+        let email = Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+            .to("Hei <hei@domain.tld>".parse().unwrap())
+            .subject("Happy new year")
+            .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
+            .body(String::from("Be happy!"))
+            .unwrap();
+
+        let result = sender.send(email).await;
+        let id = result.unwrap();
+
+        let eml_file = temp_dir().join(format!("{}.eml", id));
+        let eml = read_to_string(&eml_file).unwrap();
+
+        assert_eq!(
+            eml,
+            concat!(
+                "From: NoBody <nobody@domain.tld>\r\n",
+                "Reply-To: Yuin <yuin@domain.tld>\r\n",
+                "To: Hei <hei@domain.tld>\r\n",
+                "Subject: Happy new year\r\n",
+                "Date: Tue, 15 Nov 1994 08:12:31 GMT\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n",
+                "\r\n",
+                "Be happy!"
+            )
+        );
+        remove_file(eml_file).unwrap();
+    }
+}
+
+#[cfg(test)]
+#[cfg(all(
+    feature = "file-transport",
+    feature = "builder",
+    feature = "async-std1"
+))]
+mod asyncstd_1 {
+    use lettre::{AsyncFileTransport, AsyncStd1Executor, AsyncTransport, Message};
+    use std::{
+        env::temp_dir,
+        fs::{read_to_string, remove_file},
+    };
+
+    #[async_std::test]
+    async fn file_transport_asyncstd1() {
+        let sender = AsyncFileTransport::<AsyncStd1Executor>::new(temp_dir());
+        let email = Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+            .to("Hei <hei@domain.tld>".parse().unwrap())
+            .subject("Happy new year")
+            .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
+            .body(String::from("Be happy!"))
+            .unwrap();
+
+        let result = sender.send(email).await;
+        let id = result.unwrap();
+
+        let eml_file = temp_dir().join(format!("{}.eml", id));
+        let eml = read_to_string(&eml_file).unwrap();
+
+        assert_eq!(
+            eml,
+            concat!(
+                "From: NoBody <nobody@domain.tld>\r\n",
+                "Reply-To: Yuin <yuin@domain.tld>\r\n",
+                "To: Hei <hei@domain.tld>\r\n",
+                "Subject: Happy new year\r\n",
+                "Date: Tue, 15 Nov 1994 08:12:31 GMT\r\n",
+                "Content-Transfer-Encoding: 7bit\r\n",
+                "\r\n",
+                "Be happy!"
+            )
+        );
+        remove_file(eml_file).unwrap();
+    }
+}
diff --git a/tests/transport_sendmail.rs b/tests/transport_sendmail.rs
index dac0b0f..0f44673 100644
--- a/tests/transport_sendmail.rs
+++ b/tests/transport_sendmail.rs
@@ -1,14 +1,10 @@
 #[cfg(test)]
 #[cfg(all(feature = "sendmail-transport", feature = "builder"))]
-mod test {
-    use lettre::{transport::sendmail::SendmailTransport, Message};
-
-    #[cfg(feature = "tokio02")]
-    use tokio02_crate as tokio;
+mod sync {
+    use lettre::{Message, SendmailTransport, Transport};
 
     #[test]
     fn sendmail_transport() {
-        use lettre::Transport;
         let sender = SendmailTransport::new();
         let email = Message::builder()
             .from("NoBody <nobody@domain.tld>".parse().unwrap())
@@ -22,32 +18,20 @@ mod test {
         println!("{:?}", result);
         assert!(result.is_ok());
     }
+}
 
-    #[cfg(feature = "async-std1")]
-    #[async_std::test]
-    async fn sendmail_transport_asyncstd1() {
-        use lettre::{AsyncSendmailTransport, AsyncStd1Executor, AsyncTransport};
+#[cfg(test)]
+#[cfg(all(
+    feature = "sendmail-transport",
+    feature = "builder",
+    feature = "tokio02"
+))]
+mod tokio_02 {
+    use lettre::{AsyncSendmailTransport, AsyncTransport, Message, Tokio02Executor};
+    use tokio02_crate as tokio;
 
-        let sender = AsyncSendmailTransport::<AsyncStd1Executor>::new();
-        let email = Message::builder()
-            .from("NoBody <nobody@domain.tld>".parse().unwrap())
-            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
-            .to("Hei <hei@domain.tld>".parse().unwrap())
-            .subject("Happy new year")
-            .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body(String::from("Be happy!"))
-            .unwrap();
-
-        let result = sender.send(email).await;
-        println!("{:?}", result);
-        assert!(result.is_ok());
-    }
-
-    #[cfg(feature = "tokio02")]
     #[tokio::test]
     async fn sendmail_transport_tokio02() {
-        use lettre::{AsyncSendmailTransport, AsyncTransport, Tokio02Executor};
-
         let sender = AsyncSendmailTransport::<Tokio02Executor>::new();
         let email = Message::builder()
             .from("NoBody <nobody@domain.tld>".parse().unwrap())
@@ -63,3 +47,58 @@ mod test {
         assert!(result.is_ok());
     }
 }
+
+#[cfg(test)]
+#[cfg(all(
+    feature = "sendmail-transport",
+    feature = "builder",
+    feature = "tokio1"
+))]
+mod tokio_1 {
+    use lettre::{AsyncSendmailTransport, AsyncTransport, Message, Tokio1Executor};
+    use tokio1_crate as tokio;
+
+    #[tokio::test]
+    async fn sendmail_transport_tokio1() {
+        let sender = AsyncSendmailTransport::<Tokio1Executor>::new();
+        let email = Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+            .to("Hei <hei@domain.tld>".parse().unwrap())
+            .subject("Happy new year")
+            .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
+            .body(String::from("Be happy!"))
+            .unwrap();
+
+        let result = sender.send(email).await;
+        println!("{:?}", result);
+        assert!(result.is_ok());
+    }
+}
+
+#[cfg(test)]
+#[cfg(all(
+    feature = "sendmail-transport",
+    feature = "builder",
+    feature = "async-std1"
+))]
+mod asyncstd_1 {
+    use lettre::{AsyncSendmailTransport, AsyncStd1Executor, AsyncTransport, Message};
+
+    #[async_std::test]
+    async fn sendmail_transport_asyncstd1() {
+        let sender = AsyncSendmailTransport::<AsyncStd1Executor>::new();
+        let email = Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+            .to("Hei <hei@domain.tld>".parse().unwrap())
+            .subject("Happy new year")
+            .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
+            .body(String::from("Be happy!"))
+            .unwrap();
+
+        let result = sender.send(email).await;
+        println!("{:?}", result);
+        assert!(result.is_ok());
+    }
+}
diff --git a/tests/transport_smtp.rs b/tests/transport_smtp.rs
index bcfaa41..262eb3a 100644
--- a/tests/transport_smtp.rs
+++ b/tests/transport_smtp.rs
@@ -1,6 +1,6 @@
 #[cfg(test)]
 #[cfg(all(feature = "smtp-transport", feature = "builder"))]
-mod test {
+mod sync {
     use lettre::{Message, SmtpTransport, Transport};
 
     #[test]
@@ -12,10 +12,87 @@ mod test {
             .subject("Happy new year")
             .body(String::from("Be happy!"))
             .unwrap();
-        SmtpTransport::builder_dangerous("127.0.0.1")
+
+        let sender = SmtpTransport::builder_dangerous("127.0.0.1")
             .port(2525)
-            .build()
-            .send(&email)
-            .unwrap();
+            .build();
+        sender.send(&email).unwrap();
+    }
+}
+
+#[cfg(test)]
+#[cfg(all(feature = "smtp-transport", feature = "builder", feature = "tokio02"))]
+mod tokio_02 {
+    use lettre::{AsyncSmtpTransport, AsyncTransport, Message, Tokio02Executor};
+
+    use tokio02_crate as tokio;
+
+    #[tokio::test]
+    async fn smtp_transport_simple_tokio02() {
+        let email = Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+            .to("Hei <hei@domain.tld>".parse().unwrap())
+            .subject("Happy new year")
+            .body(String::from("Be happy!"))
+            .unwrap();
+
+        let sender: AsyncSmtpTransport<Tokio02Executor> =
+            AsyncSmtpTransport::<Tokio02Executor>::builder_dangerous("127.0.0.1")
+                .port(2525)
+                .build();
+        sender.send(email).await.unwrap();
+    }
+}
+
+#[cfg(test)]
+#[cfg(all(feature = "smtp-transport", feature = "builder", feature = "tokio1"))]
+mod tokio_1 {
+    use lettre::{AsyncSmtpTransport, AsyncTransport, Message, Tokio1Executor};
+
+    use tokio1_crate as tokio;
+
+    #[tokio::test]
+    async fn smtp_transport_simple_tokio1() {
+        let email = Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+            .to("Hei <hei@domain.tld>".parse().unwrap())
+            .subject("Happy new year")
+            .body(String::from("Be happy!"))
+            .unwrap();
+
+        let sender: AsyncSmtpTransport<Tokio1Executor> =
+            AsyncSmtpTransport::<Tokio1Executor>::builder_dangerous("127.0.0.1")
+                .port(2525)
+                .build();
+        sender.send(email).await.unwrap();
+    }
+}
+
+#[cfg(test)]
+#[cfg(all(
+    feature = "smtp-transport",
+    feature = "builder",
+    feature = "async-std1"
+))]
+mod asyncstd_1 {
+    use lettre::{AsyncSmtpTransport, AsyncStd1Executor, AsyncTransport, Message};
+
+    #[async_std::test]
+    async fn smtp_transport_simple_asyncstd1() {
+        let email = Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+            .to("Hei <hei@domain.tld>".parse().unwrap())
+            .subject("Happy new year")
+            .body(String::from("Be happy!"))
+            .unwrap();
+
+        let sender: AsyncSmtpTransport<AsyncStd1Executor> =
+            AsyncSmtpTransport::<AsyncStd1Executor>::builder_dangerous("127.0.0.1")
+                .port(2525)
+                .build();
+        sender.send(email).await.unwrap();
     }
 }
diff --git a/tests/transport_smtp_pool.rs b/tests/transport_smtp_pool.rs
index 0830a9a..fca6377 100644
--- a/tests/transport_smtp_pool.rs
+++ b/tests/transport_smtp_pool.rs
@@ -1,7 +1,6 @@
 #[cfg(all(test, feature = "smtp-transport", feature = "r2d2"))]
-mod test {
+mod sync {
     use lettre::{address::Envelope, SmtpTransport, Transport};
-
     use std::{sync::mpsc, thread};
 
     fn envelope() -> Envelope {
diff --git a/tests/transport_stub.rs b/tests/transport_stub.rs
index 6259721..db05621 100644
--- a/tests/transport_stub.rs
+++ b/tests/transport_stub.rs
@@ -1,15 +1,10 @@
 #[cfg(test)]
 #[cfg(feature = "builder")]
-mod test {
-    use lettre::{transport::stub::StubTransport, Message};
-
-    #[cfg(feature = "tokio02")]
-    use tokio02_crate as tokio;
+mod sync {
+    use lettre::{transport::stub::StubTransport, Message, Transport};
 
     #[test]
     fn stub_transport() {
-        use lettre::Transport;
-
         let sender_ok = StubTransport::new_ok();
         let sender_ko = StubTransport::new_error();
         let email = Message::builder()
@@ -23,32 +18,65 @@ mod test {
         sender_ok.send(&email).unwrap();
         sender_ko.send(&email).unwrap_err();
     }
+}
 
-    #[cfg(feature = "async-std1")]
-    #[async_std::test]
-    async fn stub_transport_asyncstd1() {
-        use lettre::AsyncTransport;
+#[cfg(test)]
+#[cfg(all(feature = "builder", feature = "tokio02"))]
+mod tokio_02 {
+    use lettre::{transport::stub::StubTransport, AsyncTransport, Message};
 
-        let sender_ok = StubTransport::new_ok();
-        let sender_ko = StubTransport::new_error();
-        let email = Message::builder()
-            .from("NoBody <nobody@domain.tld>".parse().unwrap())
-            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
-            .to("Hei <hei@domain.tld>".parse().unwrap())
-            .subject("Happy new year")
-            .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
-            .body(String::from("Be happy!"))
-            .unwrap();
+    use tokio02_crate as tokio;
 
-        sender_ok.send(email.clone()).await.unwrap();
-        sender_ko.send(email).await.unwrap_err();
-    }
-
-    #[cfg(feature = "tokio02")]
     #[tokio::test]
     async fn stub_transport_tokio02() {
-        use lettre::AsyncTransport;
-
+        let sender_ok = StubTransport::new_ok();
+        let sender_ko = StubTransport::new_error();
+        let email = Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+            .to("Hei <hei@domain.tld>".parse().unwrap())
+            .subject("Happy new year")
+            .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
+            .body(String::from("Be happy!"))
+            .unwrap();
+
+        sender_ok.send(email.clone()).await.unwrap();
+        sender_ko.send(email).await.unwrap_err();
+    }
+}
+
+#[cfg(test)]
+#[cfg(all(feature = "builder", feature = "tokio1"))]
+mod tokio_1 {
+    use lettre::{transport::stub::StubTransport, AsyncTransport, Message};
+
+    use tokio1_crate as tokio;
+
+    #[tokio::test]
+    async fn stub_transport_tokio1() {
+        let sender_ok = StubTransport::new_ok();
+        let sender_ko = StubTransport::new_error();
+        let email = Message::builder()
+            .from("NoBody <nobody@domain.tld>".parse().unwrap())
+            .reply_to("Yuin <yuin@domain.tld>".parse().unwrap())
+            .to("Hei <hei@domain.tld>".parse().unwrap())
+            .subject("Happy new year")
+            .date("Tue, 15 Nov 1994 08:12:31 GMT".parse().unwrap())
+            .body(String::from("Be happy!"))
+            .unwrap();
+
+        sender_ok.send(email.clone()).await.unwrap();
+        sender_ko.send(email).await.unwrap_err();
+    }
+}
+
+#[cfg(test)]
+#[cfg(all(feature = "builder", feature = "async-std1"))]
+mod asyncstd_1 {
+    use lettre::{transport::stub::StubTransport, AsyncTransport, Message};
+
+    #[async_std::test]
+    async fn stub_transport_asyncstd1() {
         let sender_ok = StubTransport::new_ok();
         let sender_ko = StubTransport::new_error();
         let email = Message::builder()