diff --git a/src/commands.rs b/src/commands.rs
index 491fb51..499b8a9 100644
--- a/src/commands.rs
+++ b/src/commands.rs
@@ -14,8 +14,8 @@ pub mod local;
 pub enum CommandError {
     #[error("Certificate not found: {0}")]
     CertNotFound(Fingerprint),
-    #[error("List of domains is empty")]
-    DomainListEmpty,
+    #[error("Certificate not usable: {0}")]
+    CertNotUsable(Fingerprint),
 }
 
 pub async fn dispatch(cli: CliArgs, config: HuskConfigContainer) -> Result<()> {
diff --git a/src/commands/introducer/add.rs b/src/commands/introducer/add.rs
index 2ce7dd3..695a712 100644
--- a/src/commands/introducer/add.rs
+++ b/src/commands/introducer/add.rs
@@ -1,3 +1,5 @@
+//! introducer add subcommand
+
 use anyhow::Result;
 use sequoia_cert_store::Store;
 use sequoia_openpgp::cert::ValidCert;
@@ -32,7 +34,7 @@ pub async fn dispatch(cmd: IntroducerAddCommand, config: HuskConfigContainer) ->
     if let Some(cert) = certs.first() {
         Introducer::create(&context, cert, cmd.domains)?;
     } else {
-        return Err(CommandError::CertNotFound(fpr).into());
+        return Err(CommandError::CertNotUsable(fpr).into());
     }
 
     Ok(())
diff --git a/src/commands/introducer/remove.rs b/src/commands/introducer/remove.rs
index be283e4..fc21717 100644
--- a/src/commands/introducer/remove.rs
+++ b/src/commands/introducer/remove.rs
@@ -1,3 +1,5 @@
+//! introducer remove subcommand
+
 use anyhow::Result;
 
 use sequoia_openpgp::{Fingerprint, KeyHandle};
@@ -35,7 +37,7 @@ pub async fn dispatch(cmd: IntroducerRemoveCommand, config: HuskConfigContainer)
     if let Some(cert) = certs.first() {
         Introducer::remove(&context, cert, cmd.demote)?;
     } else {
-        return Err(CommandError::CertNotFound(fpr).into());
+        return Err(CommandError::CertNotUsable(fpr).into());
     }
 
 
diff --git a/src/main.rs b/src/main.rs
index b1df41c..2f8666d 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,6 +1,4 @@
-//
-// Husk milter
-//
+//! Husk milter
 
 use std::process;
 use std::sync::{Arc, Mutex};
diff --git a/src/types/errors.rs b/src/types/errors.rs
index 5e1f66d..8e270d4 100644
--- a/src/types/errors.rs
+++ b/src/types/errors.rs
@@ -1,4 +1,4 @@
-//! Error typ
+//! Husk Error type
 
 use thiserror::Error;
 
diff --git a/src/types/introducer.rs b/src/types/introducer.rs
index 17e71de..aa20538 100644
--- a/src/types/introducer.rs
+++ b/src/types/introducer.rs
@@ -6,7 +6,6 @@ use sequoia_wot as wot;
 use wot::{CertSynopsis, Certification};
 use sequoia_openpgp::{cert::ValidCert, policy::StandardPolicy};
 use sequoia_openpgp::Cert;
-use sequoia_openpgp::Fingerprint;
 
 use crate::types::husk_context::HuskContext;
 use crate::common::crypto;
@@ -15,14 +14,6 @@ use crate::common::crypto;
 pub enum IntroducerError {
     #[error("Unsuitable certificate")]
     UnsuitableCertificate,
-    #[error("Unlimited introducer")]
-    UnlimitedIntroducer,
-    #[error("Invalid domain name: '{0}'")]
-    InvalidDomainName(String),
-    #[error("Certificate {0} contains no usable user id")]
-    NoUserIDs(Fingerprint),
-    #[error("Local trust root is damanged")]
-    RootDamaged,
 }
 
 #[derive(Debug, Clone)]
@@ -33,6 +24,10 @@ pub struct Introducer {
 
 impl Introducer {
 
+    /// Can this introducer potentially introduce `email`?
+    ///
+    /// This check matches the email with the list of domains of the
+    /// introducer.
     pub fn can_introduce(&self, email: &str) -> bool {
         if let Some(regexset) = self.certification.regular_expressions() {
             if regexset.matches_everything() {