Defaults depend on the application and actual settings depend on the admin/postmaster. So retry queues will typically be somewhere between 3 to 7 days, dependi

Defaults depend on the application and actual settings depend on the admin/postmaster. So retry queues will typically be somewhere between 3 to 7 days, depending. High volume sending servers may be shorter. It is rare for short outages to cause emails to be lost unless the outage is due to a fire and the server holding your message melted.