When a temporary failure, commonly referred to as a deferral, is encountered during the SMTP communication with the recipient mail system, the message will remain in the delivery queue for your SocketLabs server. We will retry message delivery at least once per hour for up to four days, or based on the frequency established in the customized delivery retry settings configured for your account.
If the maximum message delivery retry period has been exhausted and the message still can not be delivered, this final status and the last encountered error response will be logged in the failed messages report for your SocketLabs server.