diff --git a/back/db/imap/imap-db.ts b/back/db/imap/imap-db.ts
index 17ee942..c3c9a06 100644
--- a/back/db/imap/imap-db.ts
+++ b/back/db/imap/imap-db.ts
@@ -16,26 +16,38 @@ export async function getAllAccounts() {
     return await execQueryAsync(query, values);
 }
 
-export async function getAllMailboxes(accountId) {
-    const query = 'SELECT * FROM mailbox WHERE mailbox.account_id = ?';
+export async function getAllMailboxes(accountId: number) {
+    const query = "SELECT * FROM mailbox WHERE mailbox.account_id = ?";
     const values = [accountId];
-    return await execQueryAsync(query, values)
+    return await execQueryAsync(query, values);
 }
 
-export async function registerMailbox(accountId, mailboxName) {
+export async function registerMailbox(accountId: number, mailboxName: string) {
     const query = `INSERT INTO mailbox (account_id, mailbox_name) VALUES (?, ?)`;
     const values = [accountId, mailboxName];
     return await execQueryAsyncWithId(query, values);
 }
 
-export async function getMailbox(mailboxId) {
+export async function getMailbox(mailboxId: number) {
     const query = `SELECT * FROM mailbox WHERE mailbox_id = ?`;
     const values = [mailboxId];
     return await execQueryAsync(query, values);
 }
 
-export function updateMailbox(mailboxId, uidnext) {
+export function updateMailbox(mailboxId: number, uidnext: number) {
     const query = `UPDATE mailbox SET uidnext = ? WHERE mailbox_id = ?`;
     const values = [uidnext, mailboxId];
     execQuery(query, values);
-}
\ No newline at end of file
+}
+
+export async function updateMailboxModseq(mailboxId: number, modseq: number) {
+    const query = `UPDATE mailbox SET nextmodseq = ? WHERE mailbox_id = ?`;
+    const values = [modseq, mailboxId];
+    return await execQueryAsync(query, values);
+}
+
+export async function getMailboxModseq(mailboxId: number): Promise<{ modseq: number }[]> {
+    const query = `SELECT nextmodseq AS modseq FROM mailbox WHERE mailbox_id = ?`;
+    const values = [mailboxId];
+    return await execQueryAsync(query, values);
+}
diff --git a/back/mails/imap/Mailbox.ts b/back/mails/imap/Mailbox.ts
index 2e42a3a..3f95f53 100644
--- a/back/mails/imap/Mailbox.ts
+++ b/back/mails/imap/Mailbox.ts
@@ -1,5 +1,5 @@
 import Imap, { ImapMessageAttributes, Box } from "imap";
-import { getMailbox, updateMailbox } from "../../db/imap/imap-db";
+import { getMailbox, getMailboxModseq, updateMailbox, updateMailboxModseq } from "../../db/imap/imap-db";
 import { Attrs, AttrsWithEnvelope } from "../../interfaces/mail/attrs.interface";
 import logger from "../../system/Logger";
 import RegisterMessageInApp from "../message/saveMessage";
@@ -33,29 +33,25 @@ export default class Mailbox {
     async init() {
         // get mailbox from the database
         this.box = (await getMailbox(this.id))[0];
-
         const isReadOnly = false;
         this.imap.openBox(this.boxName, isReadOnly, (err, box) => {
             if (err) logger.err(err);
 
-            // sync only if has new messages
-            if (this.box.uidnext < box.uidnext) {
-                this.sync(this.box.uidnext, box.uidnext);
-            } else {
-                logger.log("Already up to date");
-            }
+            // sync messages and flags
+            this.initSync(box);
 
             // wait for new mails
             this.imap.on("mail", (numNewMsgs: number) => {
                 if (!this.syncing) {
                     // if not syncing restart a sync
-                    this.sync(this.box.uidnext, this.box.uidnext + numNewMsgs);
+                    this.syncMail(this.box.uidnext, this.box.uidnext + numNewMsgs);
                 } else {
                     // else save number of message to sync latter
                     this.msgToSync += numNewMsgs;
                 }
             });
 
+            // wait for flags update
             this.imap.on("update", (seqno: number, info: ImapInfo) => {
                 logger.log(`Update message ${info.uid} with ${info.flags}`);
                 const updateMsg = new updateMessage(info.uid, info.flags);
@@ -64,7 +60,43 @@ export default class Mailbox {
         });
     }
 
-    async sync(savedUid: number, currentUid: number) {
+    async updateModseq(newModseq: number) {
+        updateMailboxModseq(this.id, newModseq).then(() => {
+            this.box.highestmodseq = newModseq;
+        });
+    }
+
+    async initSync(box: Box) {
+        // sync mail only if has new messages
+        if (this.box.uidnext < box.uidnext) {
+            this.syncMail(this.box.uidnext, box.uidnext);
+        } else {
+            logger.log("Mail already up to date");
+        }
+
+        // sync flags
+        const lastModseq = (await getMailboxModseq(this.id))[0]?.modseq ?? 0;
+        if (box.highestmodseq > lastModseq) {
+            const fetchStream = this.imap.fetch("1:*", { bodies: "", modifiers: { changedsince: lastModseq } });
+            fetchStream.on("message", (message) => {
+                message.once("attributes", (attrs) => {
+                    const updateMsg = new updateMessage(attrs.uid, attrs.flags);
+                    updateMsg.updateFlags();
+                });
+            });
+            fetchStream.once("error", function (err) {
+                logger.err("Fetch error when syncing flags: " + err);
+            });
+            fetchStream.once("end", function () {
+                logger.log("Done fetching new flags");
+            });
+        } else {
+            logger.log("Flags already up to date")
+        }
+        this.updateModseq(box.highestmodseq);
+    }
+
+    async syncMail(savedUid: number, currentUid: number) {
         this.syncing = true;
         const promises: Promise<unknown>[] = [];
         const mails: Attrs[] = [];
@@ -113,7 +145,7 @@ export default class Mailbox {
                 this.box.uidnext += this.msgToSync;
                 // reset value to allow to detect new incoming message while syncing
                 this.msgToSync = 0;
-                this.sync(currentUid, this.box.uidnext);
+                this.syncMail(currentUid, this.box.uidnext);
             }
         });
     }
diff --git a/back/mails/message/updateMessage.ts b/back/mails/message/updateMessage.ts
index 5d5c7d3..b6123b3 100644
--- a/back/mails/message/updateMessage.ts
+++ b/back/mails/message/updateMessage.ts
@@ -12,7 +12,8 @@ export default class updateMessage {
     }
 
     async updateFlags() {
-        const messageId = (await getMessageIdOnUid(this.uid))[0].message_id;
+        const messageId = (await getMessageIdOnUid(this.uid))[0]?.message_id;
+        if (!messageId) return;
         const currentFlags = await getFlags(this.uid);
 
         const flagsToAdd = this.flags.filter((flag) => !currentFlags.find((f) => flag == f.flag_name));