I am using Zoho mail and I like it a lot but there are two disadvantages:

1. the free tier has no IMAP support
2. The web app for some reason doesn't allow to login to two separate accounts at the same time. Only the electron app, that's just a glorified WebView of the web app, allows multiple account support, for some reason. I have three paid accounts ($1/month) and I'm a bit annoyed by that, I have to use three different browsers or Firefox containers to switch accounts.

For the rest is excellent, the spam filter can be finely tuned in the admin panel like "block all domains like xxx" or "block all emails that contain those words". And you can set to bounce "address not found" to annoy the worst offenders that don't respect your privacy. And after a very short training (1 week!), it's very rarely wrong, unlike Gmail. If it's in spam, it's definitely spam, if it's in the inbox it's 95% ok. Unfortunately you can't block entire TLDs like .su or .monster which are exclusively used by spammers

And the webmail is very pretty and chock full of features never saw anywhere else in a web client. For example, you can add a task or add a note to an email and you can tag another user and have a parallel conversation around the content of it. Like tagging a colleague to ask opinion on that. The web client can also add IMAP accounts from other services, and you switch between them. It keeps them separate, doesn't import emails like Gmail (you can add Gmail/Hotmail/whatever but you can't add another Zoho email! Infuriating!). It's like having a "web version of thunderbird".