When an email fails to deliver, it can fail due to various reasons such as:
1. Permanent Bounce/ Hard bounce: This occurs when an email cannot be delivered due to an invalid email address or a non-existent domain. In such cases, the email server considers the bounce as permanent and won’t attempt further deliveries to that address.
2. Temporary Delivery Issue/Soft bounce: This might happen due to a full recipient mailbox, the recipient server being temporarily down, or other transient issues. In these cases, MailBluster retry sending the email after a certain period.
The rest of your emails might face temporary Delivery Issue/Soft bounce event.
When a soft bounce event happens, SES continuously retries to deliver your email for 12 hours before giving up. There is no limit of retries during this 12-hour interval and as long as the ISP recovers, your email will be delivered.
You can learn more bounce types from the AWS SES document here:
https://docs.aws.amazon.com/ses/latest/DeveloperGuide/notification-contents.html#bounce-types