It seems a bit strange that Em Client can de-Blacklist something, but doesn’t put it on a Whitelist at the same time. So the next time I get an email from the same address/domain, it’s sent to the Junk folder, because Em Client has no record of what I’ve de-blacklisted (i.e. whitelisted) in the past.
What is even the point of the “Move to Inbox and remove blacklisted email” if it doesn’t track which emails have been de-blacklisted, and apply that to all incoming future emails?
If you blacklist an address or domain using eM Client’s Blacklist feature, the address or domain will be added to the Rule, and all messages that match will be moved from Inbox to Junk. To undo this, de-blacklist and eM Client will no longer move the message to Junk.
But what usually happens is that your server moves spam messages to Junk before eM Client gets them. In that case, you will need to set the message as not spam using your provider’s webmail interface.
Yeah that’s kinda what I figured. Dumb. It makes no sense to have blacklisting without whitelisting. None. If they expect people to do whitelisting on via an email server interface, they need to enter the 21st century.
The Blacklist Rule, as with all Rules in eM Client, only applies to messages in the Inbox.
If your server has already moved the message to Junk, then eM Client has nothing to do. If you don’t want your server to manage spam filtering, then disable it on the server.
Actually, doesn’t it apply when “On Receive” ? Thus it shouldn’t matter what folder it’s in on the server; the rule should be applied when Em Client sees and downloads a new email.
Yes and no.
Rules only apply to new messages, in the Inbox. If a server-side filter has already moved the message to another folder, eM Client’s Rules will not affect it.
Are you the same Gary that replies to customer support requests from Pro users?
The same. 
I saw a very similar question in the system which I just replied to. Was that you?
Yep. For some reason I thought you were just a very enthusiastic Em Client user. Did they hire you at some point?
What’s the best way to submit a feature request to the developer?
Yes. 
I suppose I should change my profile, but I am still a very enthusiastic eM Client user, and I don’t see that changing.
You can submit it here, starting a new post and choosing the Feature Request category. That way other users can add their comments and support. Or, you can submit it through a support ticket. Either way it will be noted and added to the list of features to be considered for future development.