with v2.9.27 of SpamSieve. unchecking the rules allowed Mail to get new messages.
I moved this out of the original thread because it doesn’t sound like you’re using the macOS beta. Which version of macOS are you using, and have you tried updating to SpamSieve 2.9.28? Which Mail plug-ins are you using?
I’m using MacOS 10.12.3 on an early 2017 Macbook Pro. I tried updating to 2.9.28, but I’m getting the same results. SpamSieve is the only Mail plugin I’m using. It had been working fine until a week or two ago. The mail server is an MSExchange server. Let me know if you need more info.