What email provider do you use? Would you recommend it?

I self host. Don't.

Proton. Yes.

I used to pay for Gmail, then I used Proton Mail about a year, and I’ve been using Fastmail for the last couple of years, which I recommend. I don’t know of anything that’s as feature-rich and easy to use as Fastmail. You may not be interested in all those fancy features, though.
I use MacOS/iOS Mail clients, but also Thunderbird as I’m trying to wean myself off of Apple’s ecosystem and onto Linux/FOSS.
- +1 for fastmail… it’s one of those products that isn’t trying to trick you… you pay for it, and it’s just a solid product that tries to be the best at what it is…
  it’ll let you have as many domains and aliases as you like, including wildcards for email (and lets you reply/send appropriately using any of those aliases)
  it’ll let you pull all your calendars and push events into a single one of your choosing - it doesn’t have to be theirs
  i could probably replicate some of what it does with my home server, but it’s really nice that i don’t have to
  
  Does it have good spam filtering like Gmail?
  
  I really want to move my domain from Google to Proton, but family accounts at Proton are so dang expensive. Fastmail is far cheaper than Google, so that looks like it might be a really good option.

Protonmail, it's fantastic. Sleek design, solid feature set, integrates with Thunderbird if you want to use that.

Fastmail, 100%. Reasons:
"Encrypted email" only works between encrypted providers. ProtonMail and Tutanota are both very inconvenient, and all I want is an email that's not scanned for marketing.
Since 2018, ProtonMail kept getting worse, especially with the recent AI stuff. Dodged bullet, IMO.
$6/month = Custom domains, and any amount of emails under those domains. I can send and receive from any domain xxx@yyy [dot] lynndotpy [dot] dev, for example.
CalDav and CardDav provider = Contacts, calendar, and reminders sync. Works perfectly on iOS too, if you like that.
It replaced my finnicky NextCloud for half the cost.
- PGP encrypted e-mail works regardless of the provider btw.
  
  True but go and explain that to the regular Joe..
- You forgot the Fastmail killer feature. Masked email addresses.
- I might have to change my provider. Paying the same with a worse featureset.

ProtonMail. Works great for the most part.
Except their desktop "app", which is total shit. It's just a webview in an electron framework. If I wanted to keep a webview, I'd just keep a tab open in my browser. Or a separate browser window if I wanted to keep it separate.
- If you use the paid version of proton you can use basically any third party client (I use thunderbird)
  
  I am aware. But I feel like just a reasonable client shouldn't necessarily be considered a premium feature.
  
  This is exactly what I'm doing too.
- I've hosted my Mail with them for over a year, still have them as my backup. I wouldn't really recommend them, as they don't adhere to the standard protocols which infuriates me. As a result, you can only use a proper email client on PC with the back they call bridge, you cannot use a proper client on phones, forget syncing of calendar and contacts.
  There is more, especially for the non-mail products.
  
  as they don’t adhere to the standard protocols
  To what standards protocols do you refer? (I'm honestly asking; I'm not very knowledgeable about email architectures.)
  As a result, you can only use a proper email client on PC with the back they call bridge
  I thought that is kind of required simply due to the nature of their email service being end-to-end encrypted and with the decryption key being stored locally only.
  Am I misunderstanding something?

Mailbox.org with my own custom domain (firstname@surname.co.uk) and Thunderbird for an email client.
I would highly recommend it. It is cheap and includes almost a complete replacement for Google services (email, contacts, calendar, online drive, etc).
Please consider your privacy. Giving all you emails to Google (or other mainstream data harvesters) basically gives them deep info about your whole life (purchases, travel, communication....everything).
Having a custom domain let's you go to any provider you like if you want to switch.
- I'm with mailbox too and generally it's been pretty solid. The only thing I dislike is that their 2fa implementation is weird, and maybe that I can't get a separate password to put in my server.
  On the other hand you get a lot of solid email related things for good privacy and a pretty cheap price. They even host a thing for encrypted video calls and a document server for collaboration.

Posteo. Happy with them. For client, gnus in Emacs. Have it configured to do Autocrypt too, but almost nobody else on the planet does 🙁
- I also use posteo for four or five years now. Really happy and never had any issues so far.
- Can vouch for Posteo. I've been using them for years and I have no reason to switch anytime soon. They're privacy focused, the price is great, there's IMAP support and CalDAV too and a bunch of other things.

I self host, on a personal domain I registered in June 2000. Mostly followed a 13?-part tutorial at I think linuxbabe dot com, was the first one that seemed to genuinely be trying to help you set up a good environment, not just as a way to say “doesn’t this sound difficult? Impossible even? Coincidentally you can pay us to do this instead.” Except I put everything on its own VM instead of all on one. (Even a VM for just opendkim, which was maybe not necessary.)
Mostly iPhone mail app and/or Roundcube webmail.
Yes highly recommend it, for receiving email. Greylist blocks like 99.8% of spam. Sending works fine for me, because it’s an old domain with history. I don’t think brand new domains have the same experience.

Tuta. It's great but no third-party client support.

Proton for personal email. Not immediately needing to escape but once my free email runs out of storage I plan to switch to something else because of the concerns raised by the incident with the French climate activist.
- IIRC they warn people not to use recovery emails if they're concerned about leaking information, idk why though

Gmail and protonmail. Both give me no issues at all.

Mxroute with thunderbird as a client and mail on iOS for mobile.
Unlimited domains and rock solid. Just don’t expect lots of hand holding the company focuses on making email work you have to sort out your own details. That being said they have good documentation.
- 2nd Mxroute. I got the black Friday deal a few years ago. I love using the catchall to make emails on the fly for when I sign up for different services.
  
  I do exactly the same thing. Some more spam from time to time but usually thunderbird catches that for me.

Zoho, because it's email server is free to use for custom domain adresses

Answer to the bonus question: http://mutt.org/

My own. With blackjack and hookers.
As a client I use Kmail. But I'm not really satisfied. Kmail 3 was so great, I miss it. I should go back to Thunderbird.

Ionos.
Too lazy to selfhost. Also the implications of self hosting and securing email is too cumbersome to sleep well at night.
But I do self host non-important to my living at home.
Edit:
Inbox: Outlook. Tried eM-Client but it was worse than Outlook (around 2018 or 19)

Purely Mail, yes; so long as you're comfortable with one guy running the service.
Thunderbird for desktop and K-9 for Andriod. Only because they were the most recommended and completely fit my needs.
- Haven't had any issues with purely mail myself. I really like it
- Purely Mail has been a good experience for me so far.
- I agree, Purely Mail is great and cheap. Very cheap (I'm always afraid he's going to increase the price)
  The owner is kind and professional, but he's alone, that's the only downside.
  But if you use your own domain and you keep a backup of your messages, there's no need to worry about the one-man show.

Gmail.
No.

Migadu. Yeah*. On the computer, I use mostly aerc (+notmuch), but hop on Thunderbird once in a while; on mobile I use K-9.
If you are not looking for totally free options (though their cheapest plan is 20€/y and they give 50% discount to students), and if you don't care about email encryption (which you shouldn't). Migadu has a very good Pros/Cons page, I highly recommend you take a look, even if you're not using or planning to use their service.
- Okay you added an asterisk but I'm not seeing a footnote. Is that a markup typo?
  
  No no, it was just me being very silly and forgetting to write an important part of my comment .-.
  Fixed, thanks!
- I’m also a Migadu user. Nothing but good experiences with them. Simple, solid, and straightforward.
  
  Same. Have multiple domains and mailboxes with them, really solid. The thing I love most is probably the catch all address (allows me to effortlessly create "one-shot" addresses) and the plus-addressing automatic folders (i.e. mails to foo+bar@domain.tld automatically go to folder "bar" in mailbox "foo").

Tuta, wouldn't really recommend it since I can't use it with Thunderbird or as an SMTP server
- I tried Tuta but it felt a bit clumsy. Proton feels like it has a better UX.

gmx.com
It used to don't require phone number
I recommend it if you're not using for privacy sensitive use cases, has both IMAP and pop3 for free
- It’s been years since I’ve used their service but back then they were notorious for tricking users into signing up for their premium service with dark patterns and making it very hard to cancel. Which is why I left them and have dissuaded anyone from ever using their services.

I use gmail and my own domain with uninbox. The latter is a quite new FOSS email front/backend, but its still very new and lacks essential features.
If I'd make the switch, it would probably be to tutanota.

Proton, yes, thunderbird

Gmail, wouldn't recommend. Use it out of necessity.
I use k9 mail for checking on mobile and it is solid most of the time

I pay for a Google workspace account, but I've been thinking about self hosting. I've had my eye on mailcow for a bit, does anyone recommend?

self hosted. postfix + dovecot. android email app, thunderbird, or alpine from the cli.
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  how am i marked as a bot??? thanks. trying to fix now!