diff --git a/src/imap/command/authenticated.rs b/src/imap/command/authenticated.rs
index fca15fc..378564b 100644
--- a/src/imap/command/authenticated.rs
+++ b/src/imap/command/authenticated.rs
@@ -83,6 +83,18 @@ impl<'a> StateContext<'a> {
     S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited
     S: A142 OK [READ-WRITE] SELECT completed
 
+    --- a mailbox with no unseen message -> no unseen entry
+
+    20 select "INBOX.achats"
+    * FLAGS (\Answered \Flagged \Deleted \Seen \Draft $Forwarded JUNK $label1)
+    * OK [PERMANENTFLAGS (\Answered \Flagged \Deleted \Seen \Draft $Forwarded JUNK $label1 \*)] Flags permitted.
+    * 88 EXISTS
+    * 0 RECENT
+    * OK [UIDVALIDITY 1347986788] UIDs valid
+    * OK [UIDNEXT 91] Predicted next UID
+    * OK [HIGHESTMODSEQ 72] Highest
+    20 OK [READ-WRITE] Select completed (0.001 + 0.000 secs).
+
     * TRACE END ---
     */
     async fn select(&self, mailbox: &MailboxCodec) -> Result<(Response, flow::Transition)> {
@@ -96,8 +108,6 @@ impl<'a> StateContext<'a> {
 
         let body = vec![Data::Exists(sum.exists.try_into()?), Data::Recent(0)];
 
-        let tr = flow::Transition::Select(mb);
-
         let r_unseen = Status::ok(
             None,
             Some(Code::Unseen(
@@ -108,13 +118,22 @@ impl<'a> StateContext<'a> {
         .map_err(Error::msg)?;
         //let r_permanentflags = Status::ok(None, Some(Code::
 
+        let tr = flow::Transition::Select(mb);
+
         Ok((
             vec![
                 ImapRes::Data(Data::Exists(0)),
                 ImapRes::Data(Data::Recent(0)),
                 ImapRes::Data(Data::Flags(vec![])),
+                ImapRes::Status(
+                    Status::ok(
+                        None,
+                        Some(Code::UidValidity(sum.validity)),
+                        "UIDs valid"
+                    )
+                    .map_err(Error::msg)?,
+                ),
                 /*ImapRes::Status(),
-                ImapRes::Status(),
                 ImapRes::Status(),*/
                 ImapRes::Status(
                     Status::ok(
diff --git a/src/mailbox.rs b/src/mailbox.rs
index 249d329..54c22e3 100644
--- a/src/mailbox.rs
+++ b/src/mailbox.rs
@@ -104,7 +104,7 @@ fn dump(uid_index: &Bayou<UidIndex>) {
             "{} {} {}",
             uid,
             hex::encode(ident.0),
-            s.table.get(ident).cloned().unwrap_or_default().1.join(", ")
+            s.table.get(ident).cloned().unwrap().1.join(", ")
         );
     }
     println!("");
diff --git a/src/uidindex.rs b/src/uidindex.rs
index 8e4a189..f53d770 100644
--- a/src/uidindex.rs
+++ b/src/uidindex.rs
@@ -1,11 +1,13 @@
+use std::num::NonZeroU32;
+
 use im::{HashMap, HashSet, OrdMap, OrdSet};
 use serde::{de::Error, Deserialize, Deserializer, Serialize, Serializer};
 
 use crate::bayou::*;
 use crate::mail_ident::MailIdent;
 
-pub type ImapUid = u32;
-pub type ImapUidvalidity = u32;
+pub type ImapUid = NonZeroU32;
+pub type ImapUidvalidity = NonZeroU32;
 pub type Flag = String;
 
 #[derive(Clone)]
@@ -90,9 +92,9 @@ impl Default for UidIndex {
             table: OrdMap::new(),
             idx_by_uid: OrdMap::new(),
             idx_by_flag: FlagIndex::new(),
-            uidvalidity: 1,
-            uidnext: 1,
-            internalseq: 1,
+            uidvalidity: NonZeroU32::new(1).unwrap(),
+            uidnext: NonZeroU32::new(1).unwrap(),
+            internalseq: NonZeroU32::new(1).unwrap(),
         }
     }
 }
@@ -106,7 +108,9 @@ impl BayouState for UidIndex {
             UidIndexOp::MailAdd(ident, uid, flags) => {
                 // Change UIDValidity if there is a conflict
                 if *uid < new.internalseq {
-                    new.uidvalidity += new.internalseq - *uid;
+                    new.uidvalidity =
+                        NonZeroU32::new(new.uidvalidity.get() + new.internalseq.get() - uid.get())
+                            .unwrap();
                 }
 
                 // Assign the real uid of the email
@@ -123,7 +127,7 @@ impl BayouState for UidIndex {
                 new.reg_email(*ident, new_uid, flags);
 
                 // Update counters
-                new.internalseq += 1;
+                new.internalseq = NonZeroU32::new(new.internalseq.get() + 1).unwrap();
                 new.uidnext = new.internalseq;
             }
             UidIndexOp::MailDel(ident) => {
@@ -131,7 +135,7 @@ impl BayouState for UidIndex {
                 new.unreg_email(ident);
 
                 // We update the counter
-                new.internalseq += 1;
+                new.internalseq = NonZeroU32::new(new.internalseq.get() + 1).unwrap();
             }
             UidIndexOp::FlagAdd(ident, new_flags) => {
                 if let Some((uid, existing_flags)) = new.table.get_mut(ident) {