Hi @SumtAccen, For i). You can look at email configuration settings.
https://experienceleague.adobe.com/docs/campaign-standard/using/administrating/configuring-channels/configuring-email-channel.html?lang=en#email-processing-rules
ii). You can either do it channel level or delivery level. Look at below
documentation,
https://experienceleague.adobe.com/docs/campaign-standard/using/testing-and-sending/monitoring-messages/understanding-delivery-failures.html?lang=en#retries-after-a-delivery-tempora...