diff --git a/apps/participation/management/commands/fix_matrix_channels.py b/apps/participation/management/commands/fix_matrix_channels.py
index 764b41e..7ce878c 100644
--- a/apps/participation/management/commands/fix_matrix_channels.py
+++ b/apps/participation/management/commands/fix_matrix_channels.py
@@ -16,10 +16,8 @@ class Command(BaseCommand):
             if not os.path.isfile(".matrix_avatar"):
                 stat_file = os.stat("corres2math/static/logo.png")
                 with open("corres2math/static/logo.png", "rb") as f:
-                    resp, _ = Matrix.upload(f, filename="logo.png", content_type="image/png",
-                                            filesize=stat_file.st_size)
-                if not hasattr(resp, "content_uri"):
-                    raise Exception(resp)
+                    resp = Matrix.upload(f, filename="logo.png", content_type="image/png",
+                                         filesize=stat_file.st_size)[0][0]
                 avatar_uri = resp.content_uri
                 with open(".matrix_avatar", "w") as f:
                     f.write(avatar_uri)
@@ -58,9 +56,20 @@ class Command(BaseCommand):
                 preset=RoomPreset.public_chat,
             )
 
+        if not async_to_sync(Matrix.resolve_room_alias)("#flood:correspondances-maths.fr"):
+            Matrix.create_room(
+                visibility=RoomVisibility.public,
+                alias="flood",
+                name="Flood",
+                topic="Discutez de tout et de rien !",
+                federate=False,
+                preset=RoomPreset.public_chat,
+            )
+
         Matrix.set_room_avatar("#annonces:correspondances-maths.fr", avatar_uri)
         Matrix.set_room_avatar("#faq:correspondances-maths.fr", avatar_uri)
         Matrix.set_room_avatar("#je-cherche-une-equipe:correspondances-maths.fr", avatar_uri)
+        Matrix.set_room_avatar("#flood:correspondances-maths.fr", avatar_uri)
 
         Matrix.set_room_power_level_event("#annonces:correspondances-maths.fr", "events_default", 50)
 
@@ -69,9 +78,12 @@ class Command(BaseCommand):
             Matrix.invite("#faq:correspondances-maths.fr", f"@{r.matrix_username}:correspondances-maths.fr")
             Matrix.invite("#je-cherche-une-equipe:correspondances-maths.fr",
                           f"@{r.matrix_username}:correspondances-maths.fr")
+            Matrix.invite("#flood:correspondances-maths.fr", f"@{r.matrix_username}:correspondances-maths.fr")
 
         for admin in AdminRegistration.objects.all():
             Matrix.set_room_power_level("#annonces:correspondances-maths.fr",
                                         f"@{admin.matrix_username}:correspondances-maths.fr", 95)
             Matrix.set_room_power_level("#faq:correspondances-maths.fr",
                                         f"@{admin.matrix_username}:correspondances-maths.fr", 95)
+            Matrix.set_room_power_level("#flood:correspondances-maths.fr",
+                                        f"@{admin.matrix_username}:correspondances-maths.fr", 95)
diff --git a/apps/participation/management/commands/fix_sympa_lists.py b/apps/participation/management/commands/fix_sympa_lists.py
new file mode 100644
index 0000000..63152b5
--- /dev/null
+++ b/apps/participation/management/commands/fix_sympa_lists.py
@@ -0,0 +1,38 @@
+from corres2math.lists import get_sympa_client
+from django.core.management import BaseCommand
+from django.db.models import Q
+from participation.models import Team
+from registration.models import CoachRegistration, StudentRegistration
+
+
+class Command(BaseCommand):
+    def handle(self, *args, **options):
+        """
+        Create Sympa mailing lists and register teams.
+        """
+        sympa = get_sympa_client()
+
+        sympa.create_list("equipes", "Équipes des Correspondances", "hotline",
+                          "Liste de diffusion pour contacter toutes les équipes validées des Correspondances.",
+                          "education", raise_error=False)
+        sympa.create_list("equipes-non-valides", "Équipes des Correspondances", "hotline",
+                          "Liste de diffusion pour contacter toutes les équipes non-validées des Correspondances.",
+                          "education", raise_error=False)
+
+        for problem in range(1, 4):
+            sympa.create_list(f"probleme-{problem}",
+                              f"Équipes des Correspondances participant au problème {problem}", "hotline",
+                              f"Liste de diffusion pour contacter les équipes participant au problème {problem}"
+                              f" des Correspondances.", "education", raise_error=False)
+
+        for team in Team.objects.filter(participation__valid=True).all():
+            sympa.subscribe(team.email, "equipes", f"Equipe {team.name}", True, True)
+            sympa.subscribe(team.email, f"probleme-{team.participation.problem}", f"Equipe {team.name}", True)
+
+        for team in Team.objects.filter(Q(participation__valid=False) | Q(participation__valid__isnull=True)).all():
+            sympa.subscribe(team.email, "equipes-non-valides", f"Equipe {team.name}", True)
+
+        for student in StudentRegistration.objects.filter(team__isnull=False).all():
+            sympa.subscribe(student.user.email, f"equipe-{student.team.trigram.lower}", True, f"{student}")
+        for coach in CoachRegistration.objects.filter(team__isnull=False).all():
+            sympa.subscribe(coach.user.email, f"equipe-{coach.team.trigram.lower}", True, f"{coach}")
diff --git a/apps/participation/models.py b/apps/participation/models.py
index 8b6af3e..55e808c 100644
--- a/apps/participation/models.py
+++ b/apps/participation/models.py
@@ -65,11 +65,22 @@ class Team(models.Model):
             "education",
             raise_error=False,
         )
+        if self.pk and self.participation.valid:  # pragma: no cover
+            get_sympa_client().subscribe(self.email, "equipes", False, f"Equipe {self.name}")
+            get_sympa_client().subscribe(self.email, f"probleme-{self.participation.problem}", False,
+                                         f"Equipe {self.name}")
+        else:
+            get_sympa_client().subscribe(self.email, "equipes-non-valides", False)
 
     def delete_mailing_list(self):
         """
         Drop the Sympa mailing list, if the team is empty or if the trigram changed.
         """
+        if self.participation.valid:  # pragma: no cover
+            get_sympa_client().unsubscribe(self.email, "equipes", False)
+            get_sympa_client().unsubscribe(self.email, f"probleme-{self.participation.problem}", False)
+        else:
+            get_sympa_client().unsubscribe(self.email, "equipes-non-valides", False)
         get_sympa_client().delete_list(f"equipe-{self.trigram}")
 
     def save(self, *args, **kwargs):
@@ -281,10 +292,8 @@ class Phase(models.Model):
         qs = Phase.objects.filter(start__lte=timezone.now(), end__gte=timezone.now())
         if qs.exists():
             return qs.get()
-        qs = Phase.objects.order_by("phase_number").all()
-        if timezone.now() < qs.first().start:
-            return qs.first()
-        return qs.last()
+        qs = Phase.objects.filter(start__lte=timezone.now()).order_by("phase_number").all()
+        return qs.last() if qs.exists() else None
 
     def __str__(self):
         return _("Phase {phase_number:d} starts on {start:%Y-%m-%d %H:%M} and ends on {end:%Y-%m-%d %H:%M}")\
diff --git a/apps/participation/signals.py b/apps/participation/signals.py
index a7ee7d4..67998d9 100644
--- a/apps/participation/signals.py
+++ b/apps/participation/signals.py
@@ -2,7 +2,7 @@ from corres2math.lists import get_sympa_client
 from participation.models import Participation, Team, Video
 
 
-def create_team_participation(instance, **_):
+def create_team_participation(instance, created, **_):
     """
     When a team got created, create an associated team and create Video objects.
     """
@@ -12,6 +12,8 @@ def create_team_participation(instance, **_):
     if not participation.synthesis:
         participation.synthesis = Video.objects.create()
     participation.save()
+    if not created:
+        participation.team.create_mailing_list()
 
 
 def update_mailing_list(instance: Team, **_):
diff --git a/apps/participation/templatetags/__init__.py b/apps/participation/templatetags/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/apps/participation/templatetags/calendar.py b/apps/participation/templatetags/calendar.py
new file mode 100644
index 0000000..62cc0aa
--- /dev/null
+++ b/apps/participation/templatetags/calendar.py
@@ -0,0 +1,12 @@
+from django import template
+
+from ..models import Phase
+
+
+def current_phase(nb):
+    phase = Phase.current_phase()
+    return phase is not None and phase.phase_number == nb
+
+
+register = template.Library()
+register.filter("current_phase", current_phase)
diff --git a/apps/participation/tests.py b/apps/participation/tests.py
index 47d2ad2..b1b7bd2 100644
--- a/apps/participation/tests.py
+++ b/apps/participation/tests.py
@@ -582,7 +582,7 @@ class TestStudentParticipation(TestCase):
         for i in range(1, 5):
             Phase.objects.filter(phase_number=i).update(start=timezone.now() + timedelta(days=2 * i),
                                                         end=timezone.now() + timedelta(days=2 * i + 1))
-        self.assertEqual(Phase.current_phase().phase_number, 1)
+        self.assertEqual(Phase.current_phase(), None)
 
         # We are after the end
         for i in range(1, 5):
diff --git a/apps/participation/views.py b/apps/participation/views.py
index 7c03eb4..5534278 100644
--- a/apps/participation/views.py
+++ b/apps/participation/views.py
@@ -232,6 +232,11 @@ class TeamDetailView(LoginRequiredMixin, FormMixin, ProcessFormView, DetailView)
             mail_plain = render_to_string("participation/mails/team_validated.txt", mail_context)
             mail_html = render_to_string("participation/mails/team_validated.html", mail_context)
             send_mail("[Corres2math] Équipe validée", mail_plain, None, [self.object.email], html_message=mail_html)
+
+            get_sympa_client().subscribe(self.object.email, "equipes", False, f"Equipe {self.object.name}")
+            get_sympa_client().unsubscribe(self.object.email, "equipes-non-valides", False)
+            get_sympa_client().subscribe(self.object.email, f"probleme-{self.object.participation.problem}", False,
+                                         f"Equipe {self.object.name}")
         elif "invalidate" in self.request.POST:
             self.object.participation.valid = None
             self.object.participation.save()
diff --git a/apps/registration/fixtures/initial.json b/apps/registration/fixtures/initial.json
index 40afb61..209fc21 100644
--- a/apps/registration/fixtures/initial.json
+++ b/apps/registration/fixtures/initial.json
@@ -13,5 +13,14 @@
             "single_log_out": true,
             "single_log_out_callback": ""
         }
+    },
+    {
+        "model": "cas_server.replaceattributname",
+        "pk": 1,
+        "fields": {
+            "name": "display_name",
+            "replace": "",
+            "service_pattern": 1
+        }
     }
 ]
diff --git a/apps/registration/signals.py b/apps/registration/signals.py
index 71b761e..0a6edec 100644
--- a/apps/registration/signals.py
+++ b/apps/registration/signals.py
@@ -50,3 +50,4 @@ def invite_to_public_rooms(instance: Registration, created: bool, **_):
         Matrix.invite("#faq:correspondances-maths.fr", f"@{instance.matrix_username}:correspondances-maths.fr")
         Matrix.invite("#je-cherche-une-equip:correspondances-maths.fr",
                       f"@{instance.matrix_username}:correspondances-maths.fr")
+        Matrix.invite("#flood:correspondances-maths.fr", f"@{instance.matrix_username}:correspondances-maths.fr")
diff --git a/apps/registration/tests.py b/apps/registration/tests.py
index 4c464c9..e43aabc 100644
--- a/apps/registration/tests.py
+++ b/apps/registration/tests.py
@@ -1,3 +1,4 @@
+from datetime import timedelta
 import os
 
 from corres2math.tokens import email_validation_token
@@ -7,8 +8,10 @@ from django.contrib.sites.models import Site
 from django.core.management import call_command
 from django.test import TestCase
 from django.urls import reverse
+from django.utils import timezone
 from django.utils.encoding import force_bytes
 from django.utils.http import urlsafe_base64_encode
+from participation.models import Phase
 
 from .models import AdminRegistration, CoachRegistration, StudentRegistration
 
@@ -81,6 +84,13 @@ class TestRegistration(TestCase):
         """
         Ensure that the signup form is working successfully.
         """
+        # After first phase
+        response = self.client.get(reverse("registration:signup"))
+        self.assertEqual(response.status_code, 403)
+
+        Phase.objects.filter(phase_number__gte=2).update(start=timezone.now() + timedelta(days=1),
+                                                         end=timezone.now() + timedelta(days=2))
+
         response = self.client.get(reverse("registration:signup"))
         self.assertEqual(response.status_code, 200)
 
diff --git a/apps/registration/views.py b/apps/registration/views.py
index 91d13b6..7fe6707 100644
--- a/apps/registration/views.py
+++ b/apps/registration/views.py
@@ -13,6 +13,7 @@ from django.utils.http import urlsafe_base64_decode
 from django.utils.translation import gettext_lazy as _
 from django.views.generic import CreateView, DetailView, RedirectView, TemplateView, UpdateView, View
 from magic import Magic
+from participation.models import Phase
 
 from .forms import CoachRegistrationForm, PhotoAuthorizationForm, SignupForm, StudentRegistrationForm, UserForm
 from .models import StudentRegistration
@@ -27,6 +28,15 @@ class SignupView(CreateView):
     template_name = "registration/signup.html"
     extra_context = dict(title=_("Sign up"))
 
+    def dispatch(self, request, *args, **kwargs):
+        """
+        The signup view is available only during the first phase.
+        """
+        current_phase = Phase.current_phase()
+        if not current_phase or current_phase.phase_number >= 2:
+            raise PermissionDenied(_("You can't register now."))
+        return super().dispatch(request, *args, **kwargs)
+
     def get_context_data(self, **kwargs):
         context = super().get_context_data()
 
diff --git a/corres2math/matrix.py b/corres2math/matrix.py
index d01e44f..a6265a9 100644
--- a/corres2math/matrix.py
+++ b/corres2math/matrix.py
@@ -216,7 +216,7 @@ class Matrix:
         """
         client = await cls._get_client()
         resp = await client.room_resolve_alias(room_alias)
-        return resp.room_id if resp else None
+        return resp.room_id if resp and hasattr(resp, "room_id") else None
 
     @classmethod
     @async_to_sync
diff --git a/corres2math/templates/base.html b/corres2math/templates/base.html
index 33a0211..9a6611e 100644
--- a/corres2math/templates/base.html
+++ b/corres2math/templates/base.html
@@ -1,4 +1,4 @@
-{% load static i18n static %}
+{% load static i18n static calendar %}
 
 <!DOCTYPE html>
 {% get_current_language as LANGUAGE_CODE %}{% get_current_language_bidi as LANGUAGE_BIDI %}
@@ -126,9 +126,11 @@
                     </li>
                 {% endif %}
                 {% if not user.is_authenticated %}
-                    <li class="nav-item active">
-                        <a class="nav-link" href="{% url "registration:signup" %}"><i class="fas fa-user-plus"></i> {% trans "Register" %}</a>
-                    </li>
+                    {% if 1|current_phase %}
+                        <li class="nav-item active">
+                            <a class="nav-link" href="{% url "registration:signup" %}"><i class="fas fa-user-plus"></i> {% trans "Register" %}</a>
+                        </li>
+                    {% endif %}
                     <li class="nav-item active">
                         <a class="nav-link" href="#" data-toggle="modal" data-target="#loginModal">
                             <i class="fas fa-sign-in-alt"></i> {% trans "Log in" %}
diff --git a/locale/fr/LC_MESSAGES/django.po b/locale/fr/LC_MESSAGES/django.po
index ceaef72..984e3a1 100644
--- a/locale/fr/LC_MESSAGES/django.po
+++ b/locale/fr/LC_MESSAGES/django.po
@@ -986,7 +986,7 @@ msgstr "Réinitialiser mon mot de passe"
 #: apps/registration/templates/registration/signup.html:5
 #: apps/registration/templates/registration/signup.html:8
 #: apps/registration/templates/registration/signup.html:20
-#: apps/registration/views.py:28
+#: apps/registration/views.py:29
 msgid "Sign up"
 msgstr "Inscription"
 
@@ -1063,36 +1063,40 @@ msgid "Update user"
 msgstr "Modifier l'utilisateur"
 
 #: apps/registration/templates/registration/user_detail.html:77
-#: apps/registration/views.py:206
+#: apps/registration/views.py:216
 msgid "Upload photo authorization"
 msgstr "Téléverser l'autorisation de droit à l'image"
 
-#: apps/registration/views.py:64
+#: apps/registration/views.py:37
+msgid "You can't register now."
+msgstr "Vous ne pouvez pas vous inscrire maintenant."
+
+#: apps/registration/views.py:74
 msgid "Email validation"
 msgstr "Validation de l'adresse mail"
 
-#: apps/registration/views.py:66
+#: apps/registration/views.py:76
 msgid "Validate email"
 msgstr "Valider l'adresse mail"
 
-#: apps/registration/views.py:105
+#: apps/registration/views.py:115
 msgid "Email validation unsuccessful"
 msgstr "Échec de la validation de l'adresse mail"
 
-#: apps/registration/views.py:116
+#: apps/registration/views.py:126
 msgid "Email validation email sent"
 msgstr "Mail de confirmation de l'adresse mail envoyé"
 
-#: apps/registration/views.py:124
+#: apps/registration/views.py:134
 msgid "Resend email validation link"
 msgstr "Renvoyé le lien de validation de l'adresse mail"
 
-#: apps/registration/views.py:158
+#: apps/registration/views.py:168
 #, python-brace-format
 msgid "Detail of user {user}"
 msgstr "Détails de l'utilisateur {user}"
 
-#: apps/registration/views.py:179
+#: apps/registration/views.py:189
 #, python-brace-format
 msgid "Update user {user}"
 msgstr "Mise à jour de l'utilisateur {user}"