mail-addons/res_partner_mails_count/models.py

from openerp import models, fields, api


class ResPartner(models.Model):
    _inherit = 'res.partner'
    mails_to = fields.Integer(compute="_compute_mails_to")
    mails_from = fields.Integer(compute="_compute_mails_from")

    def _compute_mails_to(self):
        for r in self:
            r.mails_to = self.env['mail.message'].sudo().search_count([('partner_ids', 'in', r.id)])

    def _compute_mails_from(self):
        for r in self:
            r.mails_from = self.env['mail.message'].sudo().search_count([('author_id', '=', r.id)])