diff --git a/src/server/fingerd/local_email.rs b/src/server/fingerd/local_email.rs
index 4c394a0..697839c 100644
--- a/src/server/fingerd/local_email.rs
+++ b/src/server/fingerd/local_email.rs
@@ -89,3 +89,120 @@ fn detect_new_mail_by_maildir(maildir_path: &Path) -> anyhow::Result<MailStatus>
         ))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use nix::{
+        fcntl::AT_FDCWD,
+        sys::{stat::UtimensatFlags, time::TimeSpec},
+    };
+    use std::{fs, os::unix::fs::MetadataExt};
+    use tempfile::TempDir;
+
+    fn set_file_times(path: &Path, atime: i64, mtime: i64) {
+        nix::sys::stat::utimensat(
+            AT_FDCWD,
+            path,
+            &TimeSpec::new(atime, 0),
+            &TimeSpec::new(mtime, 0),
+            UtimensatFlags::FollowSymlink,
+        )
+        .unwrap();
+    }
+
+    fn set_dir_mtime(path: &Path, mtime: i64) {
+        let metadata = fs::metadata(path).unwrap();
+        set_file_times(path, metadata.atime(), mtime);
+    }
+
+    #[test]
+    fn test_detect_new_mail_by_mailbox_new_mail_received() {
+        let tempdir = TempDir::new().unwrap();
+        let mailbox = tempdir.path().join("Mailbox");
+        fs::write(&mailbox, b"mail").unwrap();
+        set_file_times(&mailbox, 1_700_000_000, 1_700_000_100);
+
+        let status = detect_new_mail_by_mailbox(&mailbox).unwrap();
+
+        assert_eq!(
+            status,
+            MailStatus::NewMailReceived {
+                received_time: Utc.timestamp_opt(1_700_000_100, 0).single().unwrap(),
+                unread_since: Utc.timestamp_opt(1_700_000_000, 0).single().unwrap(),
+            }
+        );
+    }
+
+    #[test]
+    fn test_detect_new_mail_by_mailbox_mail_last_read() {
+        let tempdir = TempDir::new().unwrap();
+        let mailbox = tempdir.path().join("Mailbox");
+        fs::write(&mailbox, b"mail").unwrap();
+        set_file_times(&mailbox, 1_700_000_100, 1_700_000_000);
+
+        let status = detect_new_mail_by_mailbox(&mailbox).unwrap();
+
+        assert_eq!(
+            status,
+            MailStatus::MailLastRead(Utc.timestamp_opt(1_700_000_100, 0).single().unwrap())
+        );
+    }
+
+    #[test]
+    fn test_detect_new_mail_by_maildir_no_mail() {
+        let tempdir = TempDir::new().unwrap();
+        let maildir = tempdir.path().join("Maildir");
+        let new_dir = maildir.join("new");
+        let cur_dir = maildir.join("cur");
+        fs::create_dir_all(&new_dir).unwrap();
+        fs::create_dir_all(&cur_dir).unwrap();
+
+        let status = detect_new_mail_by_maildir(&maildir).unwrap();
+
+        assert_eq!(status, MailStatus::NoMail);
+    }
+
+    #[test]
+    fn test_detect_new_mail_by_maildir_new_mail_received() {
+        let tempdir = TempDir::new().unwrap();
+        let maildir = tempdir.path().join("Maildir");
+        let new_dir = maildir.join("new");
+        let cur_dir = maildir.join("cur");
+        fs::create_dir_all(&new_dir).unwrap();
+        fs::create_dir_all(&cur_dir).unwrap();
+        fs::write(new_dir.join("msg"), b"mail").unwrap();
+        set_dir_mtime(&cur_dir, 1_700_000_000);
+        set_dir_mtime(&new_dir, 1_700_000_100);
+
+        let status = detect_new_mail_by_maildir(&maildir).unwrap();
+
+        assert_eq!(
+            status,
+            MailStatus::NewMailReceived {
+                received_time: Utc.timestamp_opt(1_700_000_100, 0).single().unwrap(),
+                unread_since: Utc.timestamp_opt(1_700_000_000, 0).single().unwrap(),
+            }
+        );
+    }
+
+    #[test]
+    fn test_detect_new_mail_by_maildir_mail_last_read() {
+        let tempdir = TempDir::new().unwrap();
+        let maildir = tempdir.path().join("Maildir");
+        let new_dir = maildir.join("new");
+        let cur_dir = maildir.join("cur");
+        fs::create_dir_all(&new_dir).unwrap();
+        fs::create_dir_all(&cur_dir).unwrap();
+        fs::write(cur_dir.join("msg"), b"mail").unwrap();
+        set_dir_mtime(&new_dir, 1_700_000_000);
+        set_dir_mtime(&cur_dir, 1_700_000_100);
+
+        let status = detect_new_mail_by_maildir(&maildir).unwrap();
+
+        assert_eq!(
+            status,
+            MailStatus::MailLastRead(Utc.timestamp_opt(1_700_000_100, 0).single().unwrap())
+        );
+    }
+}