I've had FastMail about a year, and have yet to get enough spam (200 messages) to trigger their personalized spam filter. Despite the address being signed up... everywhere. The non-personalized ranking system uses common spam ranking services out there, and scores emails about as well as you'd expect from the average corporate spam filter.
FastMail's data collection of your email for their own use is incredibly, incredibly limited, so a lot of things other providers use won't really work for FastMail.
Re: Zoho, when things go wrong expect days of issues and no real replies, but green status pages due to old school sharding behind the scenes (only small number of customers effected so well stay green, I.e. no mail for three days). Premium customer? Call their support number, yep a voicemail, a callback? not within 24hrs. Terrible company. Sloppy products. Dont ever recommend this to clients, even if the client is a cheapstake and 5 free accounts appeals just say 'not on my name'
Zoho Mail? Don't even get me started … We had so many laughable problems with that service. Like being unable to remove a user account because the whole management UI was just plain broken. We tried removing the account for I don't know how many months. When I let them know about the issue I got a response asking for a scan of the CEO's ID card. Finally they fixed it but then the login broke. When I tried logging in to the management UI, all I got was a redirect back to the login screen. Hell I could go on. Moved everything off to AWS WorkMail and learned my lesson.
Yep. So many WTFs. You could lock an account (and associated IMAP connector) just by paging in the web UI too fast, with users that like to page vs search to find a message this was quite a problem as they could no longer get messages via UI or their phone. When they explained this 3 days later (typical response time) I nearly fell off my chair, this was after six unanswered voicemails and a few emails (paying customer of 9 accounts I think ~ $90/m)
I wanted to try Zoho about a year ago, but couldn't even get through their sign-up process without errors that prevented completion. Never went back. First impressions and all.
It's pretty good, especially after I've trained it with enough spam & ham emails to turn on its personal ruleset - probably not as good as Google spam filter, but at least I have some visibility into why given message was misclassified.
Additionally, you can read the email's source transmission. That way you can read the SpamAssassin headers and see exactly why it was flagged ham or spam. It's been a pretty indispensable tool for email testing for my personal projects for how nifty it is.
I've noticed a few (2-3 per month) getting through with names of people in my address book, but not the email address, so it seems to be doing some type whitelisting there, other than that, its catching everything.
FastMail's data collection of your email for their own use is incredibly, incredibly limited, so a lot of things other providers use won't really work for FastMail.