Redirects are normal for site moves and retired URLs. Google treats a permanent redirect (301, 308) as a signal that the target should be canonical and documents no PageRank loss, so redirect old URLs permanently to their closest replacement to keep their links (Canonical URLs). The spam policies forbid sneaky redirects, which show "users and search engines different content", such as redirecting only mobile users to a spam domain. Doorway abuse, pages built to rank for similar queries and funnel visitors elsewhere, is a separate violation.