diff --git a/src/transport/smtp/async_transport.rs b/src/transport/smtp/async_transport.rs
index 08f5ebc..a64d598 100644
--- a/src/transport/smtp/async_transport.rs
+++ b/src/transport/smtp/async_transport.rs
@@ -147,11 +147,11 @@ where
     /// [`AsyncSmtpTransport::starttls_relay`](#method.starttls_relay) instead,
     /// if possible.
     pub fn builder_dangerous<T: Into<String>>(server: T) -> AsyncSmtpTransportBuilder {
-        let new = SmtpInfo {
+        let info = SmtpInfo {
             server: server.into(),
             ..Default::default()
         };
-        AsyncSmtpTransportBuilder { info: new }
+        AsyncSmtpTransportBuilder { info }
     }
 }
 
@@ -237,6 +237,7 @@ impl AsyncSmtpTransportBuilder {
             info: self.info,
             marker_: PhantomData,
         };
+
         AsyncSmtpTransport { inner: client }
     }
 }
diff --git a/src/transport/smtp/pool.rs b/src/transport/smtp/pool.rs
deleted file mode 100644
index 3c495a8..0000000
--- a/src/transport/smtp/pool.rs
+++ /dev/null
@@ -1,111 +0,0 @@
-use std::time::Duration;
-
-use crate::transport::smtp::{client::SmtpConnection, error, error::Error, SmtpClient};
-
-use r2d2::{CustomizeConnection, ManageConnection, Pool};
-
-/// Configuration for a connection pool
-#[derive(Debug, Clone)]
-#[allow(missing_copy_implementations)]
-#[cfg_attr(docsrs, doc(cfg(feature = "r2d2")))]
-pub struct PoolConfig {
-    min_idle: u32,
-    max_size: u32,
-    connection_timeout: Duration,
-    idle_timeout: Duration,
-}
-
-impl PoolConfig {
-    /// Create a new pool configuration with default values
-    pub fn new() -> Self {
-        Self::default()
-    }
-
-    /// Minimum number of idle connections
-    ///
-    /// Defaults to `0`
-    pub fn min_idle(mut self, min_idle: u32) -> Self {
-        self.min_idle = min_idle;
-        self
-    }
-
-    /// Maximum number of pooled connections
-    ///
-    /// Defaults to `10`
-    pub fn max_size(mut self, max_size: u32) -> Self {
-        self.max_size = max_size;
-        self
-    }
-
-    /// Connection timeout
-    ///
-    /// Defaults to `30 seconds`
-    pub fn connection_timeout(mut self, connection_timeout: Duration) -> Self {
-        self.connection_timeout = connection_timeout;
-        self
-    }
-
-    /// Connection idle timeout
-    ///
-    /// Defaults to `60 seconds`
-    pub fn idle_timeout(mut self, idle_timeout: Duration) -> Self {
-        self.idle_timeout = idle_timeout;
-        self
-    }
-
-    pub(crate) fn build<C: ManageConnection<Connection = SmtpConnection, Error = Error>>(
-        &self,
-        client: C,
-    ) -> Pool<C> {
-        Pool::builder()
-            .min_idle(Some(self.min_idle))
-            .max_size(self.max_size)
-            .connection_timeout(self.connection_timeout)
-            .idle_timeout(Some(self.idle_timeout))
-            .connection_customizer(Box::new(SmtpConnectionQuitter))
-            .build_unchecked(client)
-    }
-}
-
-impl Default for PoolConfig {
-    fn default() -> Self {
-        Self {
-            min_idle: 0,
-            max_size: 10,
-            connection_timeout: Duration::from_secs(30),
-            idle_timeout: Duration::from_secs(60),
-        }
-    }
-}
-
-impl ManageConnection for SmtpClient {
-    type Connection = SmtpConnection;
-    type Error = Error;
-
-    fn connect(&self) -> Result<Self::Connection, Error> {
-        self.connection()
-    }
-
-    fn is_valid(&self, conn: &mut Self::Connection) -> Result<(), Error> {
-        if conn.test_connected() {
-            return Ok(());
-        }
-        Err(error::network("is not connected anymore"))
-    }
-
-    fn has_broken(&self, conn: &mut Self::Connection) -> bool {
-        conn.has_broken()
-    }
-}
-
-#[derive(Copy, Clone, Debug)]
-struct SmtpConnectionQuitter;
-
-impl CustomizeConnection<SmtpConnection, Error> for SmtpConnectionQuitter {
-    fn on_release(&self, conn: SmtpConnection) {
-        let mut conn = conn;
-        if !conn.has_broken() {
-            let _quit = conn.quit();
-        }
-    }
-}
diff --git a/src/transport/smtp/pool/mod.rs b/src/transport/smtp/pool/mod.rs
new file mode 100644
index 0000000..474348f
--- /dev/null
+++ b/src/transport/smtp/pool/mod.rs
@@ -0,0 +1,67 @@
+use std::time::Duration;
+
+#[cfg(feature = "r2d2")]
+pub mod sync_impl;
+
+/// Configuration for a connection pool
+#[derive(Debug, Clone)]
+#[allow(missing_copy_implementations)]
+#[cfg_attr(docsrs, doc(cfg(any(feature = "r2d2", feature = "pool"))))]
+pub struct PoolConfig {
+    min_idle: u32,
+    max_size: u32,
+    connection_timeout: Duration,
+    idle_timeout: Duration,
+}
+
+impl PoolConfig {
+    /// Create a new pool configuration with default values
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Minimum number of idle connections
+    ///
+    /// Defaults to `0`
+    pub fn min_idle(mut self, min_idle: u32) -> Self {
+        self.min_idle = min_idle;
+        self
+    }
+
+    /// Maximum number of pooled connections
+    ///
+    /// Defaults to `10`
+    pub fn max_size(mut self, max_size: u32) -> Self {
+        self.max_size = max_size;
+        self
+    }
+
+    /// Connection timeout
+    ///
+    /// Defaults to `30 seconds`
+    #[doc(hidden)]
+    #[deprecated(note = "The Connection timeout is already configured on the SMTP transport")]
+    pub fn connection_timeout(mut self, connection_timeout: Duration) -> Self {
+        self.connection_timeout = connection_timeout;
+        self
+    }
+
+    /// Connection idle timeout
+    ///
+    /// Defaults to `60 seconds`
+    pub fn idle_timeout(mut self, idle_timeout: Duration) -> Self {
+        self.idle_timeout = idle_timeout;
+        self
+    }
+}
+
+impl Default for PoolConfig {
+    fn default() -> Self {
+        Self {
+            min_idle: 0,
+            max_size: 10,
+            connection_timeout: Duration::from_secs(30),
+            idle_timeout: Duration::from_secs(60),
+        }
+    }
+}
diff --git a/src/transport/smtp/pool/sync_impl.rs b/src/transport/smtp/pool/sync_impl.rs
new file mode 100644
index 0000000..7a3dd44
--- /dev/null
+++ b/src/transport/smtp/pool/sync_impl.rs
@@ -0,0 +1,51 @@
+use r2d2::{CustomizeConnection, ManageConnection, Pool};
+
+use super::PoolConfig;
+use crate::transport::smtp::{client::SmtpConnection, error, error::Error, SmtpClient};
+
+impl PoolConfig {
+    pub(crate) fn build<C: ManageConnection<Connection = SmtpConnection, Error = Error>>(
+        &self,
+        client: C,
+    ) -> Pool<C> {
+        Pool::builder()
+            .min_idle(Some(self.min_idle))
+            .max_size(self.max_size)
+            .connection_timeout(self.connection_timeout)
+            .idle_timeout(Some(self.idle_timeout))
+            .connection_customizer(Box::new(SmtpConnectionQuitter))
+            .build_unchecked(client)
+    }
+}
+
+impl ManageConnection for SmtpClient {
+    type Connection = SmtpConnection;
+    type Error = Error;
+
+    fn connect(&self) -> Result<Self::Connection, Error> {
+        self.connection()
+    }
+
+    fn is_valid(&self, conn: &mut Self::Connection) -> Result<(), Error> {
+        if conn.test_connected() {
+            return Ok(());
+        }
+        Err(error::network("is not connected anymore"))
+    }
+
+    fn has_broken(&self, conn: &mut Self::Connection) -> bool {
+        conn.has_broken()
+    }
+}
+
+#[derive(Copy, Clone, Debug)]
+struct SmtpConnectionQuitter;
+
+impl CustomizeConnection<SmtpConnection, Error> for SmtpConnectionQuitter {
+    fn on_release(&self, conn: SmtpConnection) {
+        let mut conn = conn;
+        if !conn.has_broken() {
+            let _quit = conn.quit();
+        }
+    }
+}