diff --git a/src/config.rs b/src/config.rs
index c1df822..62c7dad 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,5 +1,6 @@
 use crate::algorithm::Algorithm;
 use crate::canonicalization::Canonicalization;
+use anyhow::{anyhow, Result};
 use clap::Parser;
 use std::collections::HashSet;
 use std::fs::File;
@@ -39,7 +40,7 @@ pub struct Config {
 }
 
 impl Config {
-	pub fn init() -> Result<Self, String> {
+	pub fn init() -> Result<Self> {
 		let mut cnf = Self::parse();
 		cnf.key_data_base = process_key_data_base(cnf.key_data_base);
 		cnf.domain = process_domains(&cnf.domain, &cnf.domain_file)?;
@@ -116,12 +117,12 @@ fn process_key_data_base(opt: Option<PathBuf>) -> Option<PathBuf> {
 	}
 }
 
-fn process_domains(lst: &[String], domain_file: &Option<PathBuf>) -> Result<Vec<String>, String> {
+fn process_domains(lst: &[String], domain_file: &Option<PathBuf>) -> Result<Vec<String>> {
 	let mut domain_set: HashSet<String> = lst.iter().map(|e| e.to_string()).collect();
 	if let Some(path) = domain_file {
-		let f = File::open(path).map_err(|e| format!("{}: {e}", path.display()))?;
+		let f = File::open(path).map_err(|e| anyhow!("{}: {e}", path.display()))?;
 		for line in BufReader::new(f).lines() {
-			let line = line.map_err(|e| format!("{}: {e}", path.display()))?;
+			let line = line.map_err(|e| anyhow!("{}: {e}", path.display()))?;
 			let domain = line.trim();
 			if !domain.is_empty() && !domain.starts_with('#') {
 				domain_set.insert(domain.to_string().to_lowercase());
diff --git a/src/entry.rs b/src/entry.rs
index d117e06..0f46091 100644
--- a/src/entry.rs
+++ b/src/entry.rs
@@ -1,4 +1,5 @@
 use crate::stdin_reader::StdinReader;
+use anyhow::{anyhow, Result};
 use nom::bytes::streaming::{tag, take_till, take_while1};
 use nom::IResult;
 use std::sync::Arc;
@@ -32,13 +33,13 @@ impl Entry {
 		self.data == vec![b'.']
 	}
 
-	fn from_bytes(input: &[u8]) -> Result<Entry, String> {
-		let (_, entry) = parse_entry(input).map_err(|e| format!("parsing error: {e}"))?;
+	fn from_bytes(input: &[u8]) -> Result<Entry> {
+		let (_, entry) = parse_entry(input).map_err(|e| anyhow!("parsing error: {e}"))?;
 		Ok(entry)
 	}
 }
 
-pub async fn read_entry(reader_lock: Arc<RwLock<StdinReader>>) -> Option<Result<Entry, String>> {
+pub async fn read_entry(reader_lock: Arc<RwLock<StdinReader>>) -> Option<Result<Entry>> {
 	let mut reader = reader_lock.write().await;
 	log::trace!("reader lock on stdin locked");
 	let line_res = reader.read_line().await;
diff --git a/src/message.rs b/src/message.rs
index b936283..5b3d0bf 100644
--- a/src/message.rs
+++ b/src/message.rs
@@ -77,8 +77,8 @@ impl Message {
 				);
 				// TODO: sign the message using DKIM
 			}
-			Err(_) => {
-				log::error!("{}: unable to parse message", self.session_id);
+			Err(err) => {
+				log::error!("{msg_id}: unable to parse message: {err}");
 			}
 		}
 		if let Err(err) = self.print_msg().await {
diff --git a/src/parsed_message.rs b/src/parsed_message.rs
index 20705dc..1aafe69 100644
--- a/src/parsed_message.rs
+++ b/src/parsed_message.rs
@@ -1,13 +1,15 @@
+use anyhow::{anyhow, Result};
+
 pub struct ParsedMessage<'a> {
 	pub headers: Vec<ParsedHeader<'a>>,
 	pub body: &'a [u8],
 }
 
 impl<'a> ParsedMessage<'a> {
-	pub fn from_bytes(data: &'a [u8]) -> Result<Self, ()> {
+	pub fn from_bytes(data: &'a [u8]) -> Result<Self> {
 		let (mut raw_headers, body) = match data.windows(4).position(|w| w == b"\r\n\r\n") {
 			Some(body_index) => (&data[..body_index + 2], &data[body_index + 4..]),
-			None => return Err(()),
+			None => return Err(anyhow!("message body not found")),
 		};
 		let mut headers = Vec::with_capacity(128);
 		while !raw_headers.is_empty() {
@@ -25,14 +27,15 @@ fn is_wsp(c: u8) -> bool {
 	c == b' ' || c == b'\t'
 }
 
-fn header_end_pos(data: &[u8]) -> Result<usize, ()> {
+fn header_end_pos(data: &[u8]) -> Result<usize> {
 	let mut ret = 0;
 	let max_len = data.len();
 	loop {
 		ret += data[ret..]
 			.windows(2)
 			.position(|w| w == b"\r\n")
-			.ok_or(())? + 2;
+			.ok_or(anyhow!("end of header not found"))?
+			+ 2;
 		if ret >= max_len {
 			return Ok(max_len);
 		}
@@ -50,15 +53,16 @@ pub struct ParsedHeader<'a> {
 }
 
 impl<'a> ParsedHeader<'a> {
-	fn from_bytes(data: &'a [u8]) -> Result<Self, ()> {
-		let colon_pos = data.iter().position(|&w| w == b':').ok_or(())?;
+	fn from_bytes(data: &'a [u8]) -> Result<Self> {
+		let colon_pos = data
+			.iter()
+			.position(|&w| w == b':')
+			.ok_or(anyhow!("colon not found in header"))?;
 		let name = &data[..colon_pos];
 		let value = &data[colon_pos + 1..];
 		Ok(Self {
 			name,
-			name_lower: String::from_utf8(name.to_vec())
-				.map_err(|_| ())?
-				.to_lowercase(),
+			name_lower: String::from_utf8(name.to_vec())?.to_lowercase(),
 			value,
 			raw: data,
 		})