you can also use email function inside any function (button function or any function) :
this is an example for button function i used in crm module :

    def set_approve(self, cr, uid, ids,context=None):
        res_id = self.read(cr, uid, ids, ['boq_item_ids'], context)[0]['id']
        email_obj = self.pool.get('email.template')
        user_obj = self.pool.get('res.users').browse(cr, uid, uid)
        template_ids = email_obj.search(cr, uid, [('name', '=', 'Opportunity approved')])
        email = email_obj.browse(cr, uid, template_ids[0])
        email_obj.write(cr, uid, template_ids, {'email_from': email.email_from,
                                                'email_to': email.email_to,
                                                'subject': email.subject,  
                                                'body_html': email.body_html,
                                                'email_recipients': email.email_recipients})
        email_obj.send_mail(cr, uid, template_ids[0], res_id, True, context=context)
        stage_id = self.get_stageid(cr, uid, [('state', '=', 'approved')], context=context)
    a = fields.datetime.now()
        b = self.pool.get('crm.lead').read(cr, uid, ids, context=context)
    c = b[0]['date_stage_waiting']
    timedelta = 0
    if c != 0:
            DATETIME_FORMAT = "%Y-%m-%d %H:%M:%S"
            a = datetime.datetime.strptime(a, DATETIME_FORMAT)
            c = datetime.datetime.strptime(c, DATETIME_FORMAT)
            timedelta = a - c
        if stage_id:
            self.write(cr, uid, ids, {'stage_id': stage_id, 'date_stage_approved': a, 'diff_waiting': timedelta}, context=context)
        return True

NB : 1) donot forget to create email template with name as in your function

        2) configure your outgoing mail server