I run my own email server, and use a separate address per correspondent. This avoids spam entirely. I have sometimes got some spam from some addresses but simply disable that address and then the problem is gone.

That's too much time and work for 99% of users, even tech-savvy ones.

Think of it this way: lets say you value your time at $50/hour (very conservative for a tech-savvy person). If it takes an hour a month to admin that box, that's a $50/month e-mail service you have not including VPS/VM cost.

Yes, although I am not asking everyone to do it. I am only saying I do it. It is the same protocol as everyone else's email, I just set it up my own way. Other people who like to do can try this too, but I am not trying to ask everyone to do who does not want to do.

I’ve found FastMail to be my happy medium: I can give out arbitrary aliases over a couple of domains, and only have to do the config once per domain, but they take care of the actual email server part. I can then later add mailbox rules for aliases I give important senders.

Granted, the domain config would be overwhelming for my friends and family not involved in IT - even my mechanical engineer husband doesn’t quite understand what I’m doing.

Do you accept wildcards, or create a new alias in advance every time? I used to accept wildcards around turn of millenium but spam was overwhelming.

How do you stop "mainstream" providers from sending your emails to spam?

I do not accept (and never have accepted) wildcards. I create a new alias in advance every time.

I use the ISP's server for sending, and use my own server for receiving (the menu for install Exim has a "smart host" option which does this).