If you can explain — in detail — what you want in your mail folder structure and flow, I can walk you through creating that in Mail. it is not the most configurable in that regard, but not bad at all. With a few configuration tweaks, some rules to sort incoming mail and "smart" mailboxes there isn't much you cannot do relatively easily.
NOTE: I recently reverted back to Mail because of its compatibility with my database management system and new features in macOS 12 (Monterey).
