diff --git a/imap.php b/imap.php
index de3b14e..5f88848 100644
--- a/imap.php
+++ b/imap.php
@@ -8,7 +8,7 @@
 class imap
 {
   /** The mailbox string */
-  private $mailbox;
+  private $mailbox = null;
   /** The current folder in UTF-8 */
   private $curDir = "INBOX";
   /** The auto expunge feature, after deleting/moving an email */
@@ -19,10 +19,21 @@ class imap
   private static $instance = array ();
 
   /** The constructor
-      The IMAP standard port is 143, but tunnelled is 993 */
+      The IMAP standard port is 143, but SSL tunnelled is 993 */
   public function __construct ($imapserver = "localhost", $imapport = 143,
                                $username = null, $password = null,
                                $imapssl = false, $imapcertvalidate = true)
+  {
+    $this->connect ($imapserver, $imapport, $username, $password, $imapssl,
+                    $imapcertvalidate);
+  }
+
+  /** The connect can be used when extends the imap class. The constructor can
+      be override by the child class.
+      The IMAP standard port is 143, but SSL tunnelled is 993 */
+  public function connect ($imapserver = "localhost", $imapport = 143,
+                           $username = null, $password = null,
+                           $imapssl = false, $imapcertvalidate = true)
   {
     if (! function_exists ("imap_open"))
       throw new Exception ("PHP don't support IMAP. Please add it !", 500);
@@ -65,6 +76,8 @@ class imap
       The names of folders are converted in UTF-8 */
   public function foldersList ()
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $list = array_keys ($this->foldersListWithAttr ());
     natsort ($list);
     return $list;
@@ -74,6 +87,8 @@ class imap
       attributes allow to see if there is new mails in folders */
   public function foldersListWithAttr ()
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $list = imap_getmailboxes (self::$instance[$this->mailbox], $this->mailbox,
                                "*");
     $res = array ();
@@ -92,6 +107,8 @@ class imap
       The folder name must be in UTF-8. The folder must be absolute */
   public function changeFolder ($folder)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     if (! in_array ($folder, $this->foldersList ()))
       throw new Exception ("Folder not found", 404);
     $folderUTF7 = mb_convert_encoding ($folder, "UTF7-IMAP","UTF-8");
@@ -107,12 +124,16 @@ class imap
   /** Return the current folder in UTF-8 */
   public function getFolder ()
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     return $this->curDir;
   }
 
   /** Create a new folder, provided in UTF-8. The folder must be absolute */
   public function createFolder ($folder)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     if ( in_array ($folder, $this->foldersList ()))
       throw new Exception ("Folder already exists", 406);
     $folderUTF7 = mb_convert_encoding ($folder, "UTF7-IMAP","UTF-8");
@@ -124,6 +145,8 @@ class imap
     */
   public function deleteFolder ($folder)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     if (! in_array ($folder, $this->foldersList ()))
       throw new Exception ("Folder not found", 404);
     $folderUTF7 = mb_convert_encoding ($folder, "UTF7-IMAP","UTF-8");
@@ -135,6 +158,8 @@ class imap
       in UTF-8 */
   public function getSubscribe ()
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $subs = imap_getsubscribed (self::$instance[$this->mailbox], $this->mailbox,
                                 "*");
     $res = array ();
@@ -152,6 +177,8 @@ class imap
   /** Add a subscription for a folder. The folder must be in UTF-8 */
   public function addSubscribe ($folder)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $folderUTF7 = mb_convert_encoding ($folder, "UTF7-IMAP","UTF-8");
     return imap_subscribe (self::$instance[$this->mailbox],
                            $this->mailbox.$folder);
@@ -160,6 +187,8 @@ class imap
   /** Remove a subscription for a folder. The folder must be in UTF-8 */
   public function delSubscribe ($folder)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $folderUTF7 = mb_convert_encoding ($folder, "UTF7-IMAP","UTF-8");
     return imap_unsubscribe (self::$instance[$this->mailbox],
                              $this->mailbox.$folder);
@@ -177,6 +206,8 @@ class imap
         Size     mailbox size */
   public function getFolderInfo ($folder)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $oldFolder = $this->curDir;
     $this->changeFolder ($folder);
     $rc = imap_mailboxmsginfo (self::$instance[$this->mailbox]);
@@ -192,6 +223,8 @@ class imap
     /** Return an array of mailHeaders order by $field and by order ASC or DESC */
   public function imapSortMail ($mailHeaders, $field, $orderAsc = TRUE)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     $sortList = array ();
     $sortInc = array ();
@@ -219,6 +252,8 @@ class imap
       For information, takes 0.4s to select 30 mails on 1552 **/
   public function mailsDate ($from = 1, $nbmails = 30)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     if ($from === null)
       $from = 1;
@@ -264,6 +299,8 @@ class imap
       [] => array ("msgno"=>msgno, "depth"=>depth) */
   public function mailsThread ()
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     $threads = @imap_thread (self::$instance[$this->mailbox]);
     // imap_errors() takes the errors and clear the error stack
@@ -292,6 +329,8 @@ class imap
   /** Send back the number of mails in the mailbox */
   public function mailsNumber ()
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     $MC = imap_check (self::$instance[$this->mailbox]);
     return $MC->Nmsgs;
@@ -300,6 +339,8 @@ class imap
   /** Return an array containing the msgno corresponding to the criteria */
   public function mailsSearch ($criteria)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     return imap_search (self::$instance[$this->mailbox], $criteria);
   }
@@ -309,6 +350,8 @@ class imap
       Expunge automatically the current folder to remove the old emails */
   public function mailMove ($msgno, $folder)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     if (is_array ($msgno))
       $msgno = implode (",", $msgno);
@@ -327,6 +370,8 @@ class imap
       If $msgno is an array, all the mails with the contain msgno are copied */
   public function mailCopy ($msgno, $folder)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     if (is_array ($msgno))
       $msgno = implode (",", $msgno);
@@ -343,6 +388,8 @@ class imap
       needed */
   public function expunge ()
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     return imap_expunge (self::$instance[$this->mailbox]);
   }
@@ -353,6 +400,8 @@ class imap
   /** Get an existing email in the current folder in raw format */
   public function getEmailRaw ($msgno)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     // Clear the errors
     imap_errors();
@@ -367,6 +416,8 @@ class imap
   /** Get the headers of the email (in raw format) */
   public function getEmailHeadersRaw ($msgno)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     // Clear the errors
     imap_errors();
@@ -380,6 +431,8 @@ class imap
   /** Get all the body (and attached files) of an email in raw format */
   public function getEmailBodyRaw ($msgno)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     // Clear the errors
     imap_errors();
@@ -393,6 +446,8 @@ class imap
   /** Return email structure of the body */
   public function getStructure ($msgno)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     // Clear the errors
     imap_errors();
@@ -406,6 +461,8 @@ class imap
   /** Return the structure of the mail body with the associated content */
   public function getStructureWithContent ($msgno)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     // Clear the errors
     imap_errors();
@@ -532,6 +589,8 @@ class imap
       mail and some other info */
   public function getStructureContent ($msgno, $part)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $structure = $this->getStructureWithContent ($msgno);
     if (isset ($structure->parts[$part]))
       return $structure->parts[$part];
@@ -542,6 +601,8 @@ class imap
       in getStructureContent */
   public function getStructureParts ($msgno)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $structure = $this->getStructure ($msgno);
     if (! isset ($structure->parts))
       return array ();
@@ -554,6 +615,8 @@ class imap
       Expunge the mails at the end of the operation */
   public function mailsDel ($msgno)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     if (is_array ($msgno))
       $msgno = implode (",", $msgno);
@@ -571,6 +634,8 @@ class imap
       directory listing can provide erroneous data */
   public function mailAdd ($content)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $folderUTF7 = mb_convert_encoding ($this->curDir, "UTF7-IMAP","UTF-8");
     $rc = imap_append (self::$instance[$this->mailbox],
                        $this->mailbox.$folderUTF7,
@@ -588,6 +653,8 @@ class imap
   /** Return the quota used by the user in Mo */
   public function getQuota ()
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $quota = @imap_get_quotaroot (self::$instance[$this->mailbox], "INBOX");
     imap_errors();
     if (! isset ($quota["STORAGE"]))
@@ -610,6 +677,8 @@ class imap
       \Draft      Message has not completed composition (marked as a draft). */
   public function setFlag ($msgno, $flags)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     if (is_array ($msgno))
       $msgno = implode (",", $msgno);
@@ -632,6 +701,8 @@ class imap
       \Draft      Message has not completed composition (marked as a draft). */
   public function unsetFlag ($msgno, $flags)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     if (is_array ($msgno))
       $msgno = implode (",", $msgno);
@@ -648,6 +719,8 @@ class imap
       If msgno is an integer, only one mail will be modified */
   public function markMailAsRead ($msgno)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     if (is_array ($msgno))
       $msgno = implode (",", $msgno);
@@ -664,6 +737,8 @@ class imap
       If msgno is an integer, only one mail will be modified */
   public function markMailAsUnread ($msgno)
   {
+    if ($this->mailbox === null)
+      throw new Exception ("IMAP server not connected", 500);
     $this->changeFolder ($this->curDir);
     if (is_array ($msgno))
       $msgno = implode (",", $msgno);