Is it OK to prune dead inboxes (target nodes for delivery) after grace period of e.g. 7 days when transport failures (timeout, SSL, DNS, redirect loop, unresolvable host), 400, 404, 410, all 5xx occur repeatedly)?

My bots get followed by different users/nodes, but some start to show as unavailable causing my server to send requests that either hang or come back as 404s or 50Xs.