mail-addons/mail_multi_website/models/mail_thread.py

# Copyright 2018 Ivan Yelizariev <https://it-projects.info/team/yelizariev>
# License LGPL-3.0 or later (http://www.gnu.org/licenses/lgpl.html).
from odoo import models, api, tools


class MailThread(models.AbstractModel):
    _inherit = 'mail.thread'

    @api.model
    def message_route_process(self, message, message_dict, routes):
        rcpt_tos = ','.join([
            tools.decode_message_header(message, 'Delivered-To'),
            tools.decode_message_header(message, 'To'),
            tools.decode_message_header(message, 'Cc'),
            tools.decode_message_header(message, 'Resent-To'),
            tools.decode_message_header(message, 'Resent-Cc')])
        rcpt_tos_websiteparts = [e.split('@')[1].lower() for e in tools.email_split(rcpt_tos)]
        website = self.env['website'].sudo().search([
            ('domain', 'in', rcpt_tos_websiteparts)
        ])
        if website:
            self = self.with_context(website_id=website[0].id)

        return super(MailThread, self).message_route_process(
            message, message_dict, routes
        )