iMail rules are very slow After I updated my Mac to Mojave, the mail app became very slow, particularly with the rules.

I have rebuilt mailbox, restarted Mac and Mail multiple times.

My account connects to MS Exchange.

It takes ages to open rules, scroll down and add new senders to a rule I have created to mark "spam" and move all emails from this sender to junk folder. I have checked today, and to run the rule on one email takes about 1 minute. Any ideas?
I've had the same issue for Mojave and now Catalina. I've posted several 'suggestions' to Apple for improvements, especially the clunky UI, but nothing's come through yet!
The only way I know to speed things up is to move to a new, identical rule once the number of conditions grows to over 100, otherwise the interface just gums up.