The `author_id` of a `mail.mail` should always be a `res.partner` (cfr. [this line][1]). __Current behavior before commit:__ When `organizer.email` and `company.email` are empty, `author` is set to the user OdooBot instead of its corresponding partner. opw-3715380 [1]: https://github.com/odoo/odoo/blob/dcae15dcc072d14164d6454c35ce7d8d870e96ee/addons/mail/wizard/mail_compose_message.py#L107 closes odoo/odoo#153918 X-original-commit: 154de58538b89f5ac9afb9e4889240d67734beac Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>