diff --git a/src/connection/builder.rs b/src/connection/builder.rs
index 84170f6..ca7b760 100644
--- a/src/connection/builder.rs
+++ b/src/connection/builder.rs
@@ -1,20 +1,23 @@
-use super::verifier::Verifier;
-use crate::prelude::CertificateStore;
-use std::net::TcpStream;
+use super::{Verifier, FingerPrintStore};
+use rustls::ServerConfig;
+use std::{net::TcpStream, sync::Arc};
 
 #[derive(Debug)]
-pub struct Builder<S: CertificateStore> {
+pub struct Builder<S: FingerPrintStore> {
     pub stream: Option<TcpStream>,
     pub verifier: Option<Verifier<S>>,
 }
 
-impl<S: CertificateStore> Default for Builder<S> {
+impl<S: FingerPrintStore> Default for Builder<S> {
     fn default() -> Self {
-        Self { stream: None, verifier: None }
+        Self {
+            stream: None,
+            verifier: None,
+        }
     }
 }
 
-impl<S: CertificateStore> Builder<S> {
+impl<S: FingerPrintStore + 'static> Builder<S> {
     pub fn new() -> Self {
         Self::default()
     }
@@ -29,7 +32,12 @@ impl<S: CertificateStore> Builder<S> {
         self
     }
 
-    pub fn build(self) -> super::Connection {
+    pub fn build(self) -> Result<super::Connection, rustls::Error> {
+        let cfg = ServerConfig::builder()
+            .with_safe_default_cipher_suites()
+            .with_safe_default_kx_groups()
+            .with_safe_default_protocol_versions()?
+            .with_client_cert_verifier(Arc::new(self.verifier.unwrap()));
         todo!()
     }
 }
diff --git a/src/connection/error.rs b/src/connection/error.rs
index 8b13789..8680f09 100644
--- a/src/connection/error.rs
+++ b/src/connection/error.rs
@@ -1 +1,2 @@
-
+#[derive(Debug)]
+pub struct Error;
diff --git a/src/connection/mod.rs b/src/connection/mod.rs
index 7b6fecc..ea8b4f0 100644
--- a/src/connection/mod.rs
+++ b/src/connection/mod.rs
@@ -2,10 +2,11 @@ pub mod builder;
 pub mod error;
 pub mod verifier;
 
+pub use self::{builder::Builder, error::Error, verifier::{FingerPrintStore, Verifier}};
+
 #[derive(Debug)]
 pub struct Connection {
     pub inner: rustls::ServerConnection,
 }
 
-impl Connection {
-}
+impl Connection {}
diff --git a/src/connection/verifier.rs b/src/connection/verifier.rs
index e16c01a..c98bbc8 100644
--- a/src/connection/verifier.rs
+++ b/src/connection/verifier.rs
@@ -1,7 +1,30 @@
-use crate::prelude::CertificateStore;
+use rustls::server::ClientCertVerifier;
+
+use crate::{prelude::CertificateStore, mailuser::Mailuser};
 use std::sync::Mutex;
 
 #[derive(Debug)]
-pub struct Verifier<S: CertificateStore> {
+pub struct Verifier<S: FingerPrintStore> {
     pub store: Mutex<S>,
 }
+
+pub trait FingerPrintStore: Send + Sync {
+    fn get_mailuser(&self, fingerprint: &str) -> Option<Mailuser>;
+    fn insert_mailuser(&mut self, fingerprint: &str, user: &str) -> Option<Mailuser>;
+    fn contains_mailuser(&self, fingerprint: &str) -> bool;
+}
+
+impl<S: FingerPrintStore> ClientCertVerifier for Verifier<S> {
+    fn client_auth_root_subjects(&self) -> &[rustls::DistinguishedName] {
+        todo!()
+    }
+
+    fn verify_client_cert(
+            &self,
+            end_entity: &rustls::Certificate,
+            intermediates: &[rustls::Certificate],
+            now: std::time::SystemTime,
+        ) -> Result<rustls::server::ClientCertVerified, rustls::Error> {
+        todo!()
+    }
+}
diff --git a/src/mailstore/mod.rs b/src/mailstore/mod.rs
index eafe519..976217f 100644
--- a/src/mailstore/mod.rs
+++ b/src/mailstore/mod.rs
@@ -86,9 +86,7 @@ impl MailStore for Domain {
     }
 
     fn has_mailuser(&self, mailuser: &str) -> bool {
-        self.users()
-            .iter()
-            .any(|x| x.username == mailuser)
+        self.users().iter().any(|x| x.username == mailuser)
     }
 
     fn get_folder(&self, user: &str, folder: &str) -> Option<Folder> {
diff --git a/src/message/link.rs b/src/message/link.rs
index 2ee0e92..10df54f 100644
--- a/src/message/link.rs
+++ b/src/message/link.rs
@@ -27,9 +27,15 @@ impl FromStr for Link {
             return Err(super::Error::MalformedLink);
         };
         if let Some((url, display)) = s.split_once(char::is_whitespace) {
-            Ok(Self { url: url.to_string(), display: Some(display.to_string()) })
+            Ok(Self {
+                url: url.to_string(),
+                display: Some(display.to_string()),
+            })
         } else {
-            Ok(Self { url: s.to_string(), display: None })
+            Ok(Self {
+                url: s.to_string(),
+                display: None,
+            })
         }
     }
 }