diff --git a/modoboa/extensions/webmail/exceptions.py b/modoboa/extensions/webmail/exceptions.py
index f5e56cf41..51a42634a 100644
--- a/modoboa/extensions/webmail/exceptions.py
+++ b/modoboa/extensions/webmail/exceptions.py
@@ -6,14 +6,14 @@
 """
 import re
 from django.utils.translation import ugettext as _
-from modoboa.lib.exceptions import ModoboaException
+from modoboa.lib.exceptions import ModoboaException, InternalError
 
 
-class WebmailError(ModoboaException):
-    errorexpr = re.compile("\[([^\]]+)\]\s*([^\.]+)")
+class WebmailInternalError(InternalError):
+    errorexpr = re.compile(r'\[([^\]]+)\]\s*([^\.]+)')
 
     def __init__(self, reason, ajax=False):
-        match = WebmailError.errorexpr.match(reason)
+        match = WebmailInternalError.errorexpr.match(reason)
         if not match:
             self.reason = reason
         else:
@@ -24,6 +24,16 @@ class WebmailError(ModoboaException):
         return self.reason
 
 
+class UnknownAction(ModoboaException):
+    """
+    Use this exception when the webmail encounter an unknown action.
+    """
+    http_code = 404
+
+    def __init__(self):
+        super(UnknownAction, self).__init__(_("Unknown action"))
+
+
 class ImapError(ModoboaException):
     def __init__(self, reason):
         self.reason = reason
diff --git a/modoboa/extensions/webmail/imaputils.py b/modoboa/extensions/webmail/imaputils.py
index 3afa1f70a..46cdd73f2 100644
--- a/modoboa/extensions/webmail/imaputils.py
+++ b/modoboa/extensions/webmail/imaputils.py
@@ -11,9 +11,10 @@ import time
 from functools import wraps
 from django.utils.translation import ugettext as _
 from modoboa.lib import parameters, imap_utf7
+from modoboa.lib.exceptions import InternalError
 from modoboa.lib.connections import ConnectionsManager
 from modoboa.lib.webutils import static_url
-from exceptions import ImapError, WebmailError
+from exceptions import ImapError, WebmailInternalError
 from fetch_parser import parse_fetch_response
 
 #imaplib.Debug = 4
@@ -238,7 +239,7 @@ class IMAPconnector(object):
             data = self._cmd("LIST", "", "")
             m = self.list_response_pattern.match(data[0])
             if m is None:
-                raise WebmailError(_("Failed to retrieve hierarchy delimiter"))
+                raise InternalError(_("Failed to retrieve hierarchy delimiter"))
             self.__hdelimiter = m.group('delimiter')
         return self.__hdelimiter
 
@@ -564,20 +565,20 @@ class IMAPconnector(object):
             name = "%s%s%s" % (parent, self.hdelimiter, name)
         typ, data = self.m.create(self._encode_mbox_name(name))
         if typ == "NO":
-            raise WebmailError(data[0])
+            raise WebmailInternalError(data[0])
         return True
 
     def rename_folder(self, oldname, newname):
         typ, data = self.m.rename(self._encode_mbox_name(oldname),
                                   self._encode_mbox_name(newname))
         if typ == "NO":
-            raise WebmailError(data[0], ajax=True)
+            raise WebmailInternalError(data[0], ajax=True)
         return True
 
     def delete_folder(self, name):
         typ, data = self.m.delete(self._encode_mbox_name(name))
         if typ == "NO":
-            raise WebmailError(data[0])
+            raise WebmailInternalError(data[0])
         return True
 
     def getquota(self, mailbox):
diff --git a/modoboa/extensions/webmail/lib.py b/modoboa/extensions/webmail/lib.py
index 427a917d1..c31eba136 100644
--- a/modoboa/extensions/webmail/lib.py
+++ b/modoboa/extensions/webmail/lib.py
@@ -10,12 +10,13 @@ from django.core.files.uploadhandler import FileUploadHandler, SkipFile
 from django.utils.translation import ugettext as _, ugettext_lazy
 from django.conf import settings
 from modoboa.lib import u2u_decode, tables, parameters
+from modoboa.lib.exceptions import InternalError
 from modoboa.lib.webutils import size2integer
 from modoboa.lib.email_listing import EmailListing
 from modoboa.lib.emailutils import (
     EmailAddress, Email, prepare_addresses, set_email_headers
 )
-from modoboa.extensions.webmail.exceptions import WebmailError
+from modoboa.extensions.webmail.exceptions import WebmailInternalError
 from modoboa.extensions.webmail.imaputils import (
     IMAPconnector, get_imapconnector, BodyStructure
 )
@@ -562,8 +563,8 @@ def save_attachment(f):
     dstdir = os.path.join(settings.MEDIA_ROOT, "webmail")
     try:
         fp = NamedTemporaryFile(dir=dstdir, delete=False)
-    except Exception, e:
-        raise WebmailError(str(e))
+    except Exception as e:
+        raise InternalError(str(e))
     for chunk in f.chunks():
         fp.write(chunk)
     fp.close()
@@ -706,19 +707,19 @@ def send_mail(request, posturl=None):
                                  int(parameters.get_admin("SMTP_PORT")))
                 if secmode == "starttls":
                     s.starttls()
-        except Exception, text:
-            raise WebmailError(str(text))
+        except Exception as text:
+            raise WebmailInternalError(str(text))
 
         if parameters.get_admin("SMTP_AUTHENTICATION") == "yes":
             try:
                 s.login(request.user.username, get_password(request))
             except smtplib.SMTPException, e:
-                raise WebmailError(str(e))
+                raise WebmailInternalError(str(e))
         try:
             s.sendmail(request.user.email, rcpts, msg.as_string())
             s.quit()
         except smtplib.SMTPException, e:
-            raise WebmailError(str(e))
+            raise WebmailInternalError(str(e))
 
         sentfolder = parameters.get_user(request.user, "SENT_FOLDER")
         IMAPconnector(user=request.user.username,
diff --git a/modoboa/extensions/webmail/views.py b/modoboa/extensions/webmail/views.py
index 58e4c949b..a58ce7432 100644
--- a/modoboa/extensions/webmail/views.py
+++ b/modoboa/extensions/webmail/views.py
@@ -11,11 +11,12 @@ from django.contrib.auth.decorators import login_required
 from django.views.decorators.csrf import csrf_exempt
 from django.views.decorators.gzip import gzip_page
 from modoboa.lib import parameters
+from modoboa.lib.exceptions import ModoboaException, BadRequest
 from modoboa.lib.webutils import (
     _render_to_string, ajax_response, render_to_json_response
 )
 from modoboa.extensions.admin.lib import needs_mailbox
-from .exceptions import WebmailError
+from .exceptions import UnknownAction
 from .forms import FolderForm, AttachmentForm, ComposeMailForm
 from .imaputils import get_imapconnector, IMAPconnector, separate_mailbox
 from .lib import (
@@ -43,7 +44,7 @@ def getattachment(request):
     pnum = request.GET.get("partnumber", None)
     fname = request.GET.get("fname", None)
     if not mbox or not mailid or not pnum or not fname:
-        raise WebmailError(_("Invalid request"))
+        raise BadRequest(_("Invalid request"))
 
     imapc = get_imapconnector(request)
     partdef, payload = imapc.fetchpart(mailid, mbox, pnum)
@@ -61,7 +62,7 @@ def getattachment(request):
 def move(request):
     for arg in ["msgset", "to"]:
         if not arg in request.GET:
-            raise WebmailError(_("Invalid request"))
+            raise BadRequest(_("Invalid request"))
     mbc = get_imapconnector(request)
     mbc.move(request.GET["msgset"], request.session["mbox"], request.GET["to"])
     resp = listmailbox(request, request.session["mbox"], update_session=False)
@@ -74,7 +75,7 @@ def delete(request):
     mbox = request.GET.get("mbox", None)
     selection = request.GET.getlist("selection[]", None)
     if mbox is None or selection is None:
-        raise WebmailError(_("Invalid request"))
+        raise BadRequest(_("Invalid request"))
     selection = [item for item in selection if item.isdigit()]
     mbc = get_imapconnector(request)
     mbc.move(",".join(selection), mbox,
@@ -92,12 +93,12 @@ def mark(request, name):
     status = request.GET.get("status", None)
     ids = request.GET.get("ids", None)
     if status is None or ids is None:
-        raise WebmailError(_("Invalid request"))
+        raise BadRequest(_("Invalid request"))
     imapc = get_imapconnector(request)
     try:
         getattr(imapc, "mark_messages_%s" % status)(name, ids)
     except AttributeError:
-        raise WebmailError(_("Unknown action"))
+        raise UnknownAction
 
     return render_to_json_response({
         'action': status, 'mbox': name,
@@ -109,7 +110,7 @@ def mark(request, name):
 @needs_mailbox()
 def empty(request, name):
     if name != parameters.get_user(request.user, "TRASH_FOLDER"):
-        raise WebmailError(_("Invalid request"))
+        raise BadRequest(_("Invalid request"))
     get_imapconnector(request).empty(name)
     content = "<div class='alert alert-info'>%s</div>" % _("Empty mailbox")
     return render_to_json_response({
@@ -196,7 +197,7 @@ def editfolder(request, tplname="webmail/folder.html"):
 
     name = request.GET.get("name", None)
     if name is None:
-        raise WebmailError(_("Invalid request"))
+        raise BadRequest(_("Invalid request"))
     shortname, parent = separate_mailbox(name, sep=mbc.hdelimiter)
     ctx = {"title": _("Edit mailbox"),
            "formid": "mboxform",
@@ -219,7 +220,7 @@ def editfolder(request, tplname="webmail/folder.html"):
 def delfolder(request):
     name = request.GET.get("name", None)
     if name is None:
-        raise WebmailError(_("Bad request"))
+        raise BadRequest(_("Invalid request"))
     mbc = IMAPconnector(user=request.user.username,
                         password=request.session["password"])
     mbc.delete_folder(name)
@@ -251,7 +252,7 @@ def attachments(request, tplname="webmail/attachments.html"):
                     "status": "ok", "fname": request.FILES["attachment"],
                     "tmpname": os.path.basename(tmpname)
                 })
-            except WebmailError, inst:
+            except ModoboaException as inst:
                 error = _("Failed to save attachment: ") + str(inst)
 
         if csuploader.toobig:
@@ -413,7 +414,7 @@ def compose_and_send(request, action, callback=None):
     mbox = request.GET.get("mbox", None)
     mailid = request.GET.get("mailid", None)
     if mbox is None or mailid is None:
-        raise WebmailError(_("Bad request"))
+        raise BadRequest(_("Invalid request"))
     url = "?action=%s&mbox=%s&mailid=%s" % (action, mbox, mailid)
     if request.method == "POST":
         status, resp = send_mail(request, url)
@@ -447,7 +448,7 @@ def getmailcontent(request):
     mbox = request.GET.get("mbox", None)
     mailid = request.GET.get("mailid", None)
     if mbox is None or mailid is None:
-        raise WebmailError(_("Invalid request"))
+        raise BadRequest(_("Invalid request"))
     email = ImapEmail(mbox, mailid, request, links=int(request.GET["links"]))
     return render(request, "common/viewmail.html", {
         "headers": email.render_headers(folder=mbox, mail_id=mailid),
@@ -460,7 +461,7 @@ def viewmail(request):
     mbox = request.GET.get("mbox", None)
     mailid = request.GET.get("mailid", None)
     if mbox is None or mailid is None:
-        raise WebmailError(_("Invalid request"))
+        raise BadRequest(_("Invalid request"))
     links = request.GET.get("links", None)
     if links is None:
         links = 1 if parameters.get_user(request.user, "ENABLE_LINKS") == "yes" else 0
@@ -489,7 +490,7 @@ def submailboxes(request):
 def check_unseen_messages(request):
     mboxes = request.GET.get("mboxes", None)
     if not mboxes:
-        raise WebmailError(_("Invalid request"))
+        raise BadRequest(_("Invalid request"))
     mboxes = mboxes.split(",")
     counters = dict()
     imapc = get_imapconnector(request)
@@ -526,11 +527,11 @@ def index(request):
 
     if action is not None:
         if not action in globals():
-            raise WebmailError(_("Undefined action"))
+            raise UnknownAction
         response = globals()[action](request)
     else:
         if request.is_ajax():
-            raise WebmailError(_("Bad request"))
+            raise BadRequest(_("Invalid request"))
         response = dict(selection="webmail")
 
     curmbox = request.session.get("mbox", "INBOX")