mail-addons/mail_sent/models.py

from odoo import api, fields, models


class MailMessage(models.Model):
    _inherit = "mail.message"

    sent = fields.Boolean(
        "Sent", compute="_compute_sent", help="Was message sent to someone", store=True
    )

    @api.depends("author_id", "partner_ids", "channel_ids")
    def _compute_sent(self):
        for r in self:
            r_sudo = r.sudo()
            recipient_ids = r_sudo.partner_ids
            author_id = r_sudo.author_id
            res_id = (
                r_sudo.model
                and r_sudo.res_id
                and r_sudo.env[r_sudo.model].browse(r_sudo.res_id)
            )
            sent = author_id and (
                len(recipient_ids) > 1
                or (len(recipient_ids) == 1 and recipient_ids[0].id != author_id.id)
                or (len(r_sudo.channel_ids))
                or (res_id and len(res_id.message_partner_ids - author_id) > 0)
            )
            r.sent = sent

    def message_format(self):
        message_values = super(MailMessage, self).message_format()
        message_index = {message["id"]: message for message in message_values}
        for item in self:
            msg = message_index.get(item.id)
            if msg:
                msg["sent"] = item.sent
        return message_values


class MailComposeMessage(models.TransientModel):

    _inherit = "mail.compose.message"
    sent = fields.Boolean("Sent", help="dummy field to fix inherit error")