diff --git a/src/lib.rs b/src/lib.rs
index e9f7377..381411a 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -125,15 +125,15 @@
 //!
 
 pub mod smtp;
+use std::net::IpAddr;
 use std::{fmt::Display, hash::Hash, time::Duration};
-use tokio::io::{AsyncRead, AsyncWrite};
-use tokio_rustls::TlsConnector;
-
-#[cfg(feature = "builder")]
-pub use mail_builder;
 
 #[cfg(feature = "dkim")]
 pub use mail_auth;
+#[cfg(feature = "builder")]
+pub use mail_builder;
+use tokio::io::{AsyncRead, AsyncWrite};
+use tokio_rustls::TlsConnector;
 
 #[derive(Debug)]
 pub enum Error {
@@ -201,10 +201,11 @@ pub struct SmtpClientBuilder<T: AsRef<str> + PartialEq + Eq + Hash> {
     pub tls_hostname: T,
     pub tls_implicit: bool,
     pub credentials: Option<Credentials<T>>,
-    pub addr: String,
+    pub addr: Option<IpAddr>,
     pub is_lmtp: bool,
     pub say_ehlo: bool,
     pub local_host: String,
+    pub port: u16,
 }
 
 /// SMTP client builder
diff --git a/src/smtp/builder.rs b/src/smtp/builder.rs
index 56f1808..3f8f544 100644
--- a/src/smtp/builder.rs
+++ b/src/smtp/builder.rs
@@ -8,8 +8,10 @@
  * except according to those terms.
  */
 
+use crate::{Credentials, SmtpClient, SmtpClientBuilder};
 use smtp_proto::{EhloResponse, EXT_START_TLS};
 use std::hash::Hash;
+use std::net::IpAddr;
 use std::time::Duration;
 use tokio::{
     io::{AsyncRead, AsyncWrite},
@@ -17,14 +19,21 @@ use tokio::{
 };
 use tokio_rustls::client::TlsStream;
 
-use crate::{Credentials, SmtpClient, SmtpClientBuilder};
-
 use super::{tls::build_tls_connector, AssertReply};
 
 impl<T: AsRef<str> + PartialEq + Eq + Hash> SmtpClientBuilder<T> {
     pub fn new(hostname: T, port: u16) -> Self {
+        SmtpClientBuilder::_new(hostname, None, port)
+    }
+
+    pub fn new_bind_ip(hostname: T, addr: IpAddr, port: u16) -> Self {
+        SmtpClientBuilder::_new(hostname, Some(addr), port)
+    }
+
+    fn _new(hostname: T, addr: Option<IpAddr>, port: u16) -> Self {
         SmtpClientBuilder {
-            addr: format!("{}:{}", hostname.as_ref(), port),
+            addr,
+            port,
             timeout: Duration::from_secs(60 * 60),
             tls_connector: build_tls_connector(false),
             tls_hostname: hostname,
@@ -85,7 +94,7 @@ impl<T: AsRef<str> + PartialEq + Eq + Hash> SmtpClientBuilder<T> {
     pub async fn connect(&self) -> crate::Result<SmtpClient<TlsStream<TcpStream>>> {
         tokio::time::timeout(self.timeout, async {
             let mut client = SmtpClient {
-                stream: TcpStream::connect(&self.addr).await?,
+                stream: self.tcp_connect().await?,
                 timeout: self.timeout,
             };
 
@@ -130,14 +139,21 @@ impl<T: AsRef<str> + PartialEq + Eq + Hash> SmtpClientBuilder<T> {
         .map_err(|_| crate::Error::Timeout)?
     }
 
+    pub async fn tcp_connect(&self) -> std::io::Result<TcpStream> {
+        let port = self.port;
+        if let Some(addr) = self.addr {
+            TcpStream::connect((addr, port)).await
+        } else {
+            TcpStream::connect((self.tls_hostname.as_ref(), port)).await
+        }
+    }
+
     /// Connect over clear text (should not be used)
     pub async fn connect_plain(&self) -> crate::Result<SmtpClient<TcpStream>> {
         let mut client = SmtpClient {
-            stream: tokio::time::timeout(self.timeout, async {
-                TcpStream::connect(&self.addr).await
-            })
-            .await
-            .map_err(|_| crate::Error::Timeout)??,
+            stream: tokio::time::timeout(self.timeout, async { self.tcp_connect().await })
+                .await
+                .map_err(|_| crate::Error::Timeout)??,
             timeout: self.timeout,
         };