🗃️(models) add MailDomain, MailDomainAccess and Mailbox models

Additional app and models to handle email addresses creation in Desk.

src/backend/mailbox_manager/models.py

@@ -0,0 +1,88 @@
+"""
+Declare and configure the models for the People additional application : mailbox_manager
+"""
+
+from django.conf import settings
+from django.core import validators
+from django.db import models
+from django.utils.translation import gettext_lazy as _
+
+from core.models import BaseModel, RoleChoices
+
+
+class MailDomain(BaseModel):
+    """Domain names from which we will create email addresses (mailboxes)."""
+
+    name = models.CharField(
+        _("name"), max_length=150, null=False, blank=False, unique=True
+    )
+
+    class Meta:
+        db_table = "people_mail_domain"
+        verbose_name = _("Mail domain")
+        verbose_name_plural = _("Mail domains")
+
+    def __str__(self):
+        return self.name
+
+
+class MailDomainAccess(BaseModel):
+    """Allow to manage users' accesses to mail domains."""
+
+    user = models.ForeignKey(
+        settings.AUTH_USER_MODEL,
+        on_delete=models.CASCADE,
+        related_name="mail_domain_accesses",
+        null=False,
+        blank=False,
+    )
+    domain = models.ForeignKey(
+        MailDomain,
+        on_delete=models.CASCADE,
+        related_name="mail_domain_accesses",
+        null=False,
+        blank=False,
+    )
+    role = models.CharField(
+        max_length=20, choices=RoleChoices.choices, default=RoleChoices.MEMBER
+    )
+
+    class Meta:
+        db_table = "people_mail_domain_accesses"
+        verbose_name = _("User/mail domain relation")
+        verbose_name_plural = _("User/mail domain relations")
+        unique_together = ("user", "domain")
+
+    def __str__(self):
+        return f"Access of user {self.user!s} on domain {self.domain:s}."
+
+
+class Mailbox(BaseModel):
+    """Mailboxes for users from mail domain."""
+
+    local_part = models.CharField(
+        _("local_part"),
+        max_length=150,
+        null=False,
+        blank=False,
+        validators=[validators.RegexValidator(regex="^[a-zA-Z0-9_.+-]+$")],
+    )
+    domain = models.ForeignKey(
+        MailDomain,
+        on_delete=models.CASCADE,
+        related_name="mail_domain",
+        null=False,
+        blank=False,
+    )
+    secondary_email = models.EmailField(
+        _("secondary email address"), null=False, blank=False
+    )
+
+    class Meta:
+        db_table = "people_mail_box"
+        verbose_name = _("Mailbox")
+        verbose_name_plural = _("Mailboxes")
+        unique_together = ("local_part", "domain")
+
+    def __str__(self):
+        return f"{self.local_part!s}@{self.domain.name:s}."