social/mass_mailing_resend/models/mailing_mailing.py

# Copyright 2017-2020 Tecnativa - Pedro M. Baeza
# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl.html).


from odoo import _, exceptions, models


class MailingMailing(models.Model):
    _inherit = "mailing.mailing"

    def button_draft(self):
        """Return to draft state for resending the mass mailing."""
        if any(self.mapped(lambda x: x.state != "done")):
            raise exceptions.UserError(
                _(
                    "You can't resend a mass mailing that is being sent or in "
                    "draft state."
                )
            )
        self.write({"state": "draft"})