We use the delivery rate to find out how many email messages have reached our subscribers' inboxes.
To calculate it we only need to know how many emails we have sent, subtract those that have bounced and divide the result by the total number of messages sent.
Approximately 20% of mass mailings sent do not reach their destination for various reasons (bounces, anti-spam filters, faulty addresses, etc.) A good deliverability rate is generally considered to be above 95%, ideally between 98% and 99%. We must always consider that approximate 20% error.