diff --git a/src/imap/flow.rs b/src/imap/flow.rs
index 72d9e8e..e817e77 100644
--- a/src/imap/flow.rs
+++ b/src/imap/flow.rs
@@ -25,6 +25,18 @@ pub enum State {
     Idle(Arc<User>, MailboxView, MailboxPerm, Tag<'static>, Arc<Notify>),
     Logout,
 }
+impl fmt::Display for State {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use State::*;
+        match self {
+            NotAuthenticated => write!(f, "NotAuthenticated"),
+            Authenticated(..) => write!(f, "Authenticated"),
+            Selected(..) => write!(f, "Selected"),
+            Idle(..) => write!(f, "Idle"),
+            Logout => write!(f, "Logout"),
+        }
+    }
+}
 
 #[derive(Clone)]
 pub enum MailboxPerm {
@@ -41,13 +53,29 @@ pub enum Transition {
     Unselect,
     Logout,
 }
+impl fmt::Display for Transition {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        use Transition::*;
+        match self {
+            None => write!(f, "None"),
+            Authenticate(..) => write!(f, "Authenticated"),
+            Select(..) => write!(f, "Selected"),
+            Idle(..) => write!(f, "Idle"),
+            UnIdle => write!(f, "UnIdle"),
+            Unselect => write!(f, "Unselect"),
+            Logout => write!(f, "Logout"),
+        }
+    }
+}
 
 // See RFC3501 section 3.
 // https://datatracker.ietf.org/doc/html/rfc3501#page-13
 impl State {
     pub fn apply(&mut self, tr: Transition) -> Result<(), Error> {
-        let new_state = match (std::mem::replace(self, State::NotAuthenticated), tr) {
-            (_s, Transition::None) => return Ok(()),
+        tracing::debug!(state=%self, transition=%tr, "try change state");
+
+        let new_state = match (std::mem::replace(self, State::Logout), tr) {
+            (s, Transition::None) => s,
             (State::NotAuthenticated, Transition::Authenticate(u)) => State::Authenticated(u),
             (
                 State::Authenticated(u) | State::Selected(u, _, _),
@@ -63,10 +91,13 @@ impl State {
                 State::Selected(u, m, p)
             },
             (_, Transition::Logout) => State::Logout,
-            _ => return Err(Error::ForbiddenTransition),
+            (s, t) => {
+                tracing::error!(state=%s, transition=%t, "forbidden transition");
+                return Err(Error::ForbiddenTransition)
+            }
         };
-
         *self = new_state;
+        tracing::debug!(state=%self, "transition succeeded");
 
         Ok(())
     }