Implicit keep works. Explicit keep works. Fileinto works. Discard works. Redirect appears to work (not yet tested with a full mail stack).
Reject merely discards, but it should also return an appropriate rejection exit code (smtp) or 5xx code (lmtp). I'm working on vacation and subaddress this evening. More tonight. Subaddress is broken in libSieve 2.1.8. I'll post a fixed 2.1.9 tomorrow. Aaron
