As others have noted, do the trial before parting with any money.
If you want a basic email program then something like Thunderbird might do you, its getting better with its UX/UI, has tags, rules etc, and its free of course.
Outlook is another one, but you get ads if you don’t have a 365 subscription. Your own POP/IMAP accounts won’t be able to do rules without an exchange server on a Mac. Also, no categories for POP/IMAP.
eM Client is more like Outlook but doesn’t need an exchange server to do all those things.
The downside of eM Client are potential ongoing costs. If you buy the 50% personal version you will still need to purchase upgrades later on unless you want to buy the lifetime upgrade. Given the experience of Postbox dying would one want to take the risk in doing a lifetime payment? Some are fed up of paying for programs that a free one, like Thunderbird, could do, and money you would spend on eM Client could go somewhere else.
For me, the migration was a mess. Postbox Topics went to Tags, not only the UX/UI of them was ugly but it can take a while to delete them and replace them. Also rules weren’t migrated properly, basically I had to start again. It took me about 48 hours or so to get to a point where I have things under control in eM Client. Unlike going from Legacy Outlook to New Outlook I didn’t see any data loss in emails, however, do a backup in Postbox before you migrate to eM Client. eM Client categories are useless to me, can’t customize them.
The VIP support wasn’t that helpful, they told me to do things without telling me how, getting rid of me quickly I expect. The training piece from Postbox → eM Client is missing somewhat and I had to cobble around before I found things on YouTube or here in the forum.
Regarding your spam maybe you can block emails, domains or top level domains on your ISP back end before they reach your inbox. Depends who your ISP is.