Odoo already has an Email Queue Manager and this can be found under Scheduled Actions in General Settings. Normally non-forced mails will be in a queue and force send mail will send immediately. For eg: mail_obj.create() function will create mail record to send and this will be in a queue and you can see that under Emails in general settings. You can force send this mail by mail_obj.send() method. If you are sending mail using a template, then you can use force_send=True Parameter in the send_mail function. eg: template_id.send_mail(force_send=False)