Simon 5 is coming soon!
Simon version 5 is currently in beta testing. It is a massive update, introducing a much-requested feature: syncing the Simon data between multiple Macs, plus a Simon Status service, a Link Checker filter, improved Find filter, iMessage and Speak Error notifiers, a new app icon, and much more.
Important: please note that Simon 5 requires a minimum of macOS 10.12 (Sierra), and will be a paid upgrade from Simon 4 after the beta. Purchasers since September 1, 2020 automatically get a version 5 license (that also works in previous versions).
Re: Email Cycle Check not retrieving via IMAP
I'm sorry this isn't working properly for you. Using 4.3b1 shouldn't have changed anything, as it is using the same mail helper as 4.2 and earlier. Exactly the same, as I was unable to get it to rebuild.
I actually spent a number of frustrating hours last night trying to get it to build, so I could investigate this issue for you. But I failed. Apparently the recent versions of the Xcode development tools have changed the way embedded frameworks are supported (i.e. not), and I couldn't figure out any way to make it work. It's a chain of dependencies: Simon uses a mail service plugin, which in turn uses a bundled helper app, which in turn uses a third-party framework, which in turn depends on other libraries. Quite complicated, and apparently fragile to Apple's whims.
I don't have more time to investigate this now, so I'll have to come back to it for a future update. If I can't figure out a solution to building the helper, I might have to remove the Cycle service. Having a component that I can't update is not great.
If it continues to not work, all I can suggest is that you try reverting the Simon data to a backup from before trying 4.3b1, in case it somehow changed in the update. I'd be interested to know if that works.