Recommendations for an email provider?

Having great difficulty getting Better Email to work.
I've tried Gmail and Yahoo multiple times in various Better Email configurations.
With multiple configurations the errors vary but are generally "Error connecting to IMAP server: [AUTHENTICATIONFAILED] Invalid credentials (Failure)" type.

Reading through this board it appears that email providers implement different protocols for unknown(?) reasons. So I can understand better, can someone briefly explain what is *generally* happening here? I didn't post log excerpts because I think I need and umbrella view here first.

And before I chase my tail any more, What Email providers have proven to work reliability, (or at all)? Maybe I should start there.

The problems with Gmail and iCloud and similar are that most of them are moving to 2FA (2 factor authentication), with some process in place to authorize "apps" to access the service. I've gotten iCloud to work reliably with app-specific passwords. I don't use Gmail much, so I don't have any real advice there.

However, I don't use any of those services for my personal email account. I use RackSpace for my email provider. They now charge $2.99 per account, $10 min per month. I'm on their old grandfathered plan which was originally $10/mo for 5 accounts. It's now $12, so I pay $2.40 each for 5.

I've also had decent success with gmx.com. Their IMAP server seems to drop connections more than RackSpace does, but it's free.

Fastmail 100%

https://www.fastmail.com/values/

https://www.fastmail.com/privacy-and-security/

They offer MFA and app tokens for integrations among a slew of other nerdy, customizable features.

SOLVED
Thanks FlyingDriver that was it
I had been working with 4 free email providers and they all had similar AUTHENTICATION FAILED issues. I therefore assumed that it was a configuration problem on my end, I took WagnerOne's recommendation and tried Fastmail. I've been playing with it for a week and it has been ROCK SOLID.

So it occurs me you get what you pay for with free email. Fastmail will be $5/month, but will definitely be worth it if it is reliable.

Thanks again FlyingDriver and WagnerOne

and FWIW, you can also go whole hog and pay for a hosting plan on any number of hosting providers. You'll get your own domain name, and generally as many email addresses as you like. I've had several, but am using Hostgator at the moment. Just be aware of the fine print. Most advertise super low rates, but that's only if you pay for a few years of service up front. This isn't the answer for everyone, but for about $4.00 a month, I can host as many domains as I like with as many email addresses as I need, and they all work just fine with Indigo.

and FWIW, you can also go whole hog and pay for a hosting plan on any number of hosting providers. You'll get your own domain name, and generally as many email addresses as you like. I've had several, but am using Hostgator at the moment. Just be aware of the fine print. Most advertise super low rates, but that's only if you pay for a few years of service up front. This isn't the answer for everyone, but for about $4.00 a month, I can host as many domains as I like with as many email addresses as I need, and they all work just fine with Indigo.

Unfortunately, the mail servers provided with most generic hosting plans aren't very good. Specifically, their spam filtering isn't very good. A good commercial email provider will have much better spam blockers in place. IMO.