@MacExpert asked the same question 5-1/2 years ago and the only response was from @mina, who stated that “Similar services get access to 100% of your emails” (I’m not sure what that entails) and “Their pricing is not cheap and comparable to Sanebox. So you might consider Sanebox as well being an older player in the market.”
Much has changed since then. Clean Email says they were founded in Ukraine 11 years ago but are now a U.S. based company. A yearly plan to cover all of my email accounts would cost $49.99. Sanebox would cost $300.
I had Sanebox for one account, back when they were regular sponsors of all things MacSparky, but it didn’t make sense to have it for just one of my email accounts and I didn’t feel I could justify the additional cost of having it for all three.
Mailstrom, at $99 per annum, appears to be another player in the space. Of the three, Clean Email is the bargain.