Been using Zoho with multiple domains for many years. I have a business account and a personal account (and an admin account) in Zoho fed from maybe ten domains. DNS on Google cloud.

Zoho is almost never down - can't remember the last time - but they do tend to tinker stupidly occasionally. Logging in to the web is page after page of stupid questions - ok it's three but they're pushing their authentication app I don't ever want. There's PassKey but it doesn't understand Linux/Bitwarden AFAICT. I use 2fa with Bitwarden. Documentation is good but there can be multiple pages on the same subject sometimes.

Client mobile app is great. Admin mobile app is crap. Costs c. £60 a year which I think is good value given the ability to white page, (excessive) filters and automation*, mailing lists etc. Finding where you set an email address up is a bastard so take notes but they are eager to help if you can't find it.

I usually get pissed off with suppliers after a couple years of being jerked around. I've been with Zoho email for an easy decade maybe one and a half. It was definitely this century .. but .. !

I'm very privacy minded, at least one of the domains is a addy.io proxy, but never seen any indication that my/client data is being sold. Spam malware is very tight and you can admin that to within an inch of its life in miriad of ways.

Comes with all the bells and whistles you'd expect on the client end and on the server end. IMAP POP3 sure but I use the Zoho mobile client and web for all the features (tagging, priority etc) that Thunderbird won't grok.

Zoho had a deserved poor rep many years ago for going up and down like a tart's drawers but it's been nothing but up that I've noticed in the last 5 years.

I have no affiliation with any company mentioned.

I hosted my first email server in c.1996 on 14kbps before email admin became a full time job. I feel your pain.

• I have the usual delay (real) send on my business account and a couple of delete after X days triggered by my addy.io . Logic can mix AND and OR with parentheses without a limit I have hit.

If you want free, I'd recommend Protom Mail.

For paid, I really like Mailbox.org and Posteo. They work with IMAP/POP3, CardDAV, and CalDAV

I'm using Zoho. It's pretty cheap and wasn't hard to set up with my domain.

I have been using purelymail with my own domains, and at $10 a year with no limit on domains or users under those domains, it’s amazing value.

Using Fastmail

• works with 1Password to generate masked emails
• plus and subdomain addressing

In case those features are important to you

posteo is really cheap but a great service

If you want free tier with good privacy practices, Proton is going to be the best option.

I have several paid webhost accounts already, so I just use those for email. Any important messages (which are increasingly rare) are saved to PDF and stored offline (business/tax/medical info, etc.), and the rest is purged once read/sent.

I am using proton essentials plan it gets you ten custom emails that you can use with three custom domains.

So I use one email for my game servers so those services use that then I have another general use email for sending info like recently added plex content or alerts from my server then a few mix and match for random stuff.

Not the cheapest but now I'm also using their calendar which is nice. I don't use any desktop clients though I prefer to keep as much stuff in the browser

Proton, Tuta, Mailbox, and Posteo are all good.

Proton and Tuta have free offerings. Posteo and mailbox have the cheapest paid offering, but posteo doesn't allow custom domains.

I have started using Mailbox.org since about a year with several custom domains. Its around 3 €/$ per month for the basic tier which also includes some cloud storage and an online office suite (of which neither I use). I've been happy with it.

Some services Ive been looking at:

• Cheapest seems to be namecheaps own offerings: https://www.namecheap.com/hosting/email/
• Proton mail seems to be good, but I would have to pay extra for the Thunderbird integration by the look of things.

Mxroute.com look for a discount offer since they have lots of good ones.

I have several addresses at cock.li. Uptime is not the best, around 98%, but free. According to their policy they don't collect any personal data, but they comply with legal requests. https://cock.li/help

You can select from a lot of domains, some of them ar normal like firemail.cc or airmail.cc, some of them are funny like aaathats3as.com, some of them are edgy like cocaine.ninja or national.shitposting.agency, some of them are racist like nuke.africa or hitler.rocks

I use migadu.com now, previously also used mailbox.org and protonmail.
The great part with migadu is how much control you have. Want to add multiple domains or have multiple users? No problem. (Though they reserve the right to ask what you're doing if it's excessive).
Limits are based on mails sent, mails received and storage space.
I was on their cheapest plan (19$/year) until I filled my receiving contingent because my servers had issues and monitoring kept dutifully sending email alerts about that.

I'm using Proton mail, I like their focus on privacy and e2e (only with other Proton users, though).

About a year ago, I trialed both Proton Mail and Tuta mail. Proton mail worked out better for my needs, but YMMV. 

One nice thing about switching providers is that it gives you the opportunity to rid yourself of years of built-up cruft and spam.

I’m using UberSpace for 5€/month for a few small web projects and for emails. Unlimited mailboxes, unlimited aliases. However, you have to configure it using console commands via SSH. But it’s all explained in their documentation.