This is very encouraging!
Coming from Apple Mail and PostBox, I was very disgruntled to find that the developers here refused to support SpamSieve as a plug-in.
I wish that was something they would reconsider. I used to talk with the SpamSieve developer all the time and he would constantly talk with the email developers and improve his plug-in to work with their clients.
In the meantime, I have a Mac Studio that runs 24/7. I keep Apple Mail with SpamSieve running in the background so at least that is helping control all the spam that would make its way into eMClient (since the emails sync with each other). That is the only suggestion I can give at the moment in running a spam filter.
I do hope that, in the future, the developers here will reconsider their policy on allowing plug-ins. At least SpamSieve is safe and reputable.
I’m with ZaGenie but only have about 70 accounts. 
Same thing though. Some accounts it pulls daily, while others it pulls every minute.
I have a ton of smart filters to help me easily identify messages and the smart filters are applied to not just a single account, but to multiple accounts or account groups.
I have rules as well that flag, tag, file, trash, etc. messages based on fairly deep conditional logic.
These are all important. The keyboard shortcuts are as well as I hate moving over to the mouse. I don’t play Quake, Doom or COD w/ a mouse, why should I do it with email. 
There are so many things that Postbox does brilliantly and I’ve got over 7,000,000 messages indexed - unfortunately 126,000 unread in one of my groups, but…I can make quick work of these with filters and rules.
Filters are also smart - ie they are executed based on rules.
I’m sure I’ll discover more as I play with eMClient but I want to work with it, not play.
Also, when sending a message, it takes quite a while while a popup comes up and freezes all other email activity until that process is complete instead of doing it in the background. I’m sure I must have some setting wrong here.
But advanced nested conditional logic on rules is hugely critical when you are running lean and wanting to optimize workflows.
Not sure if this is helpful. I’m more than happy to zoom and show you how I work if it’d be helpful.
John
when sending a message, it takes quite a while while a popup comes up and freezes all other email activity until that process is complete instead of doing it in the background
The email normally sends like receiving without any popup message and does send in the background.
Sounds like you might have “Show Operations Window” enabled. Go to “Menu / Settings (Preferences) / General” and make sure the Show window on send and receive is not checked as in the below example.
If that is already not checked, then do a screenshot example of the sending popup you see.
I was a Postbox user for several years for my business accounts and I am very disappointed that Postbox is sold. Switching to em Client did take a few days until everything worked good for me.
People who complain about the discontinuation of Postbox forget, however, that the program has not been developed further for years. And it did have problems. It couldn’t work with Exchange servers, it couldn’t use groups of Apple Contacts, it stopped working with GPG more than a year ago (via Enigmail). These are things that em Client can do.
Postbox had a clearer interface, but in the end I can do everything I need with em Client. But em Client also has a few bugs (above all, my mail address is often written in the address field when replying – strange behavior).
Can you do an example screenshot of where it shows your email address when replying. Blank out your email address username & anything else personal.
But em Client also has a few bugs.
Can you list the other bugs / problems you are referring to.
I have been using EM for a few weeks now and have it configured just right for me. I have four accounts - a work IMAP, plus a Gmail, Outlook and Yahoo.
So I am not really a power user as such. I am really enjoying it. It is fast and stable and looks nice. I find it actually a pleasure to use and have got to grips with the Rules situation which workss well. I have yet to find it unable to do anythhing that Postbox could, butt like I said I am not a power user.
I knew that Postbox was on its way out and over the past year I have trialed a few clients, such as Canary, Mailbird, Outlook, Spark - EM is the only one I enjoyed using. I was reluctant to go back to Thunderbird, which I did use for years, although I thoroughly approve of Moziilla and have used Firefox as main browser since it was Firebird. Postbox seemed like a better version of Thunderbird and it was decent enough.
I have paid for the full version with lifetime upgrades. I feel like I found my brand and can just get on with things now.
I have no problem with paying for software that I like. And I dont really want a subscription.
I am still using Spark on my iPad, but changed to EM on my Android phone. I am not happy with that as its slow and clunky but I look forward to a better version before too long.