diff --git a/modoboa/extensions/webmail/forms.py b/modoboa/extensions/webmail/forms.py
index c377fc91b..2ff9d3ff0 100644
--- a/modoboa/extensions/webmail/forms.py
+++ b/modoboa/extensions/webmail/forms.py
@@ -14,6 +14,7 @@ from .lib import (
     ImapEmail, create_mail_attachment
 )
 
+from validators import validate_email_list
 
 def html2plaintext(content):
     """HTML to plain text translation.
@@ -76,13 +77,14 @@ def make_body_images_inline(body):
     return lxml.html.tostring(html), parts
 
 
+
 class ComposeMailForm(forms.Form):
 
     """Compose mail form."""
 
-    to = forms.CharField(label=_("To"))
-    cc = forms.CharField(label=_("Cc"), required=False)
-    cci = forms.CharField(label=_("Cci"), required=False)
+    to = forms.CharField(label=_("To"), validators=[validate_email_list])
+    cc = forms.CharField(label=_("Cc"), required=False, validators=[validate_email_list])
+    cci = forms.CharField(label=_("Cci"), required=False, validators=[validate_email_list])
     subject = forms.CharField(
         label=_("Subject"),
         max_length=255,
diff --git a/modoboa/extensions/webmail/templates/webmail/compose.html b/modoboa/extensions/webmail/templates/webmail/compose.html
index 4fb607529..06db8600f 100644
--- a/modoboa/extensions/webmail/templates/webmail/compose.html
+++ b/modoboa/extensions/webmail/templates/webmail/compose.html
@@ -8,7 +8,7 @@
       <div class="form-group{% if form.errors.to %} has-error{% endif %}">
         <label class="col-sm-1 control-label" for="id_to">{% trans "To" %}</label>
         <div class="col-sm-8">
-          <input id="id_to" name="to" class="form-control" value="{% if form.to.value %}{{ form.to.value }}{% endif %}"{% if form.to.errors %} placeholder="{% for error in form.to.errors %}{{ error }}{% endfor %}"{% endif %}>
+          <input id="id_to" name="to" class="form-control" value="{% if form.to.value %}{{ form.to.value }}{% endif %}"{% if form.to.errors %} placeholder="{% for error in form.to.errors %}{{ error }}{% endfor %}" title="{% for error in form.to.errors %}{{ error }}{% endfor %}"{% endif %}>
         </div>
         {% if not form.cc.value %}
         <div class="col-sm-2">
diff --git a/modoboa/extensions/webmail/validators.py b/modoboa/extensions/webmail/validators.py
new file mode 100644
index 000000000..8c6c25dc1
--- /dev/null
+++ b/modoboa/extensions/webmail/validators.py
@@ -0,0 +1,17 @@
+from django.utils.encoding import force_text
+from django.utils.deconstruct import deconstructible
+from django.core.validators import validate_email
+from email.utils import getaddresses
+
+class EmailListValidator(object):
+    """
+    Validate a comma separated list of email
+    """
+    def __call__(self, value):
+        value = force_text(value)
+        emails = map(unicode.strip, value.split(','))
+        addresses = getaddresses(emails)
+        [ validate_email(e) for r, e in addresses ]
+
+validate_email_list = EmailListValidator()
+