diff --git a/src/message/header/mod.rs b/src/message/header/mod.rs
index 5e0a025..687cdf7 100644
--- a/src/message/header/mod.rs
+++ b/src/message/header/mod.rs
@@ -26,6 +26,9 @@ mod mailbox;
 mod special;
 mod textual;
 
+/// Represents an email header
+///
+/// Email header as defined in [RFC5322](https://datatracker.ietf.org/doc/html/rfc5322) and extensions.
 pub trait Header: Clone {
     fn name() -> HeaderName;
 
diff --git a/src/message/header/special.rs b/src/message/header/special.rs
index 1929bac..4b5ea01 100644
--- a/src/message/header/special.rs
+++ b/src/message/header/special.rs
@@ -10,6 +10,9 @@ pub struct MimeVersion {
     minor: u8,
 }
 
+/// MIME version 1.0
+///
+/// Should be used in all MIME messages.
 pub const MIME_VERSION_1_0: MimeVersion = MimeVersion::new(1, 0);
 
 impl MimeVersion {
diff --git a/src/transport/smtp/authentication.rs b/src/transport/smtp/authentication.rs
index 36b766b..0a3799b 100644
--- a/src/transport/smtp/authentication.rs
+++ b/src/transport/smtp/authentication.rs
@@ -4,6 +4,7 @@ use crate::transport::smtp::error::{self, Error};
 use std::fmt::{self, Debug, Display, Formatter};
 
 /// Accepted authentication mechanisms
+///
 /// Trying LOGIN last as it is deprecated.
 pub const DEFAULT_MECHANISMS: &[Mechanism] = &[Mechanism::Plain, Mechanism::Login];
 
diff --git a/src/transport/smtp/client/async_connection.rs b/src/transport/smtp/client/async_connection.rs
index d3114d9..2d459bb 100644
--- a/src/transport/smtp/client/async_connection.rs
+++ b/src/transport/smtp/client/async_connection.rs
@@ -298,7 +298,7 @@ impl AsyncSmtpConnection {
                     return if response.is_positive() {
                         Ok(response)
                     } else {
-                        Err(error::code(response.code))
+                        Err(error::code(response.code()))
                     }
                 }
                 Err(nom::Err::Failure(e)) => {
diff --git a/src/transport/smtp/client/connection.rs b/src/transport/smtp/client/connection.rs
index 25676de..e73b50c 100644
--- a/src/transport/smtp/client/connection.rs
+++ b/src/transport/smtp/client/connection.rs
@@ -276,7 +276,7 @@ impl SmtpConnection {
                     return if response.is_positive() {
                         Ok(response)
                     } else {
-                        Err(error::code(response.code))
+                        Err(error::code(response.code()))
                     };
                 }
                 Err(nom::Err::Failure(e)) => {
diff --git a/src/transport/smtp/extension.rs b/src/transport/smtp/extension.rs
index 3ea4195..2c88126 100644
--- a/src/transport/smtp/extension.rs
+++ b/src/transport/smtp/extension.rs
@@ -72,6 +72,7 @@ impl ClientId {
 /// Supported ESMTP keywords
 #[derive(PartialEq, Eq, Hash, Copy, Clone, Debug)]
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
+#[non_exhaustive]
 pub enum Extension {
     /// 8BITMIME keyword
     ///
@@ -107,11 +108,11 @@ pub struct ServerInfo {
     /// Server name
     ///
     /// The name given in the server banner
-    pub name: String,
+    name: String,
     /// ESMTP features supported by the server
     ///
     /// It contains the features supported by the server and known by the `Extension` module.
-    pub features: HashSet<Extension>,
+    features: HashSet<Extension>,
 }
 
 impl Display for ServerInfo {
@@ -135,7 +136,7 @@ impl ServerInfo {
 
         let mut features: HashSet<Extension> = HashSet::new();
 
-        for line in response.message.as_slice() {
+        for line in response.message() {
             if line.is_empty() {
                 continue;
             }
@@ -197,6 +198,11 @@ impl ServerInfo {
         }
         None
     }
+
+    /// The name given in the server banner
+    pub fn name(&self) -> &str {
+        self.name.as_ref()
+    }
 }
 
 /// A `MAIL FROM` extension parameter
diff --git a/src/transport/smtp/mod.rs b/src/transport/smtp/mod.rs
index fb62409..7292f2e 100644
--- a/src/transport/smtp/mod.rs
+++ b/src/transport/smtp/mod.rs
@@ -148,7 +148,7 @@ pub mod extension;
 mod pool;
 pub mod response;
 mod transport;
-pub mod util;
+pub(super) mod util;
 
 // Registered port numbers:
 // https://www.iana.
@@ -164,7 +164,7 @@ pub const SUBMISSION_PORT: u16 = 587;
 pub const SUBMISSIONS_PORT: u16 = 465;
 
 /// Default timeout
-pub const DEFAULT_TIMEOUT: Duration = Duration::from_secs(60);
+const DEFAULT_TIMEOUT: Duration = Duration::from_secs(60);
 
 #[derive(Debug, Clone)]
 struct SmtpInfo {
diff --git a/src/transport/smtp/response.rs b/src/transport/smtp/response.rs
index 7993803..a780aae 100644
--- a/src/transport/smtp/response.rs
+++ b/src/transport/smtp/response.rs
@@ -137,10 +137,10 @@ impl Code {
 #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct Response {
     /// Response code
-    pub code: Code,
+    code: Code,
     /// Server response string (optional)
     /// Handle multiline responses
-    pub message: Vec<String>,
+    message: Vec<String>,
 }
 
 impl FromStr for Response {
@@ -180,6 +180,16 @@ impl Response {
     pub fn first_line(&self) -> Option<&str> {
         self.message.first().map(String::as_str)
     }
+
+    /// Response code
+    pub fn code(&self) -> Code {
+        self.code
+    }
+
+    /// Server response string (array of lines)
+    pub fn message(&self) -> impl Iterator<Item = &str> {
+        self.message.iter().map(String::as_str)
+    }
 }
 
 // Parsers (originally from tokio-smtp)
diff --git a/src/transport/smtp/util.rs b/src/transport/smtp/util.rs
index 959a210..44bef0c 100644
--- a/src/transport/smtp/util.rs
+++ b/src/transport/smtp/util.rs
@@ -4,7 +4,6 @@ use std::fmt::{Display, Formatter, Result as FmtResult};
 
 /// Encode a string as xtext
 #[derive(Debug)]
-#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
 pub struct XText<'a>(pub &'a str);
 
 impl<'a> Display for XText<'a> {