When emails are sent they are either accepted by the recipient mail server or a failure is reported.
If the failure is "permanent" the reports will show a bounce. Envoke will not attempt to send these emails again.
If the recipient's email server reports an error using an error code that classifies it as a "transient" failure then email sending is retried automatically over a 48-hour period up to 10 times. These emails aren't reported as bounced (soft bounce or hard bounce) during the resend period.
This is handled by our SMTP server, not visible from the interface. Retries cost no credits, and messages in the retry queue are indistinguishable from successfully sent messages until the retries are finished and a bounce is reported if the retries were unsuccessful.