diff --git a/Entities/Customer.php b/Entities/Customer.php
new file mode 100644
index 0000000..1a16936
--- /dev/null
+++ b/Entities/Customer.php
@@ -0,0 +1,18 @@
+<?php
+/*
+ SPDX-License-Identifier: AGPL-3.0-only
+ SPDX-FileCopyrightText: © 2024 Millions Missing FRANCE <info@millionsmissing.fr>
+ */
+
+namespace Modules\MMFCustomersGroups\Entities;
+
+use App\Customer as BaseCustomer;
+
+class Customer extends BaseCustomer {
+	/**
+	 * Get the groups this Customer belongs to.
+	 */
+	public function groups() {
+		return $this->belongsToMany(CustomersGroup::class);
+	}
+}
diff --git a/Entities/CustomersGroup.php b/Entities/CustomersGroup.php
new file mode 100644
index 0000000..75b70f4
--- /dev/null
+++ b/Entities/CustomersGroup.php
@@ -0,0 +1,25 @@
+<?php
+/*
+ SPDX-License-Identifier: AGPL-3.0-only
+ SPDX-FileCopyrightText: © 2024 Millions Missing FRANCE <info@millionsmissing.fr>
+ */
+
+namespace Modules\MMFCustomersGroups\Entities;
+
+use Illuminate\Database\Eloquent\Model;
+
+class CustomersGroup extends Model {
+	/**
+	 * Get the Mailbox this group is linked to.
+	 */
+	public function mailbox() {
+		return $this->belongsTo(Mailbox::class);
+	}
+
+	/**
+	 * Get the Customers that are included in this group.
+	 */
+	public function customers() {
+		return $this->belongsToMany(Customer::class);
+	}
+}
diff --git a/Entities/Mailbox.php b/Entities/Mailbox.php
new file mode 100644
index 0000000..72a13e9
--- /dev/null
+++ b/Entities/Mailbox.php
@@ -0,0 +1,18 @@
+<?php
+/*
+ SPDX-License-Identifier: AGPL-3.0-only
+ SPDX-FileCopyrightText: © 2024 Millions Missing FRANCE <info@millionsmissing.fr>
+ */
+
+namespace Modules\MMFCustomersGroups\Entities;
+
+use App\Mailbox as BaseMailbox;
+
+class Mailbox extends BaseMailbox {
+	/**
+	 * Get the customers groups linked to this Mailbox.
+	 */
+	public function groups() {
+		return $this->hasMany(CustomersGroup::class);
+	}
+}