I'm quite happy with Migadu for own domain use. I have a dozen that are unlikely to receive email but good to be able to receive them nonethelrss - migadu is great for that as you can add as many domains as you want.

Calendar feature is sorely missing though it seems this service also doesn't have it. I guess calendar is a pain to set up/troubleshoot timezone issues, etc

I think they have calendar the show how to set it up here, they just dont have a GUI for it https://www.migadu.com/guides/thunderbird/

I've also been happy with mxroute.com which has super low cost promos every November (black friday) so I'm on a $15/year plan. Regular pricing starts at $45/year for unlimited domains and mailboxes, 10GB storage.

MXroute is super awesome for device based email. If you have firewalls, copiers, system notifications, backup alerts, etc. it’s a great fit.

The killer features are unlimited mailboxes and per-mailbox quotas. I make a new mailbox for every device and give them a quota that makes sense; 10 messages per day for most. If a device goes haywire, gets compromised, or gets stolen, it’s one mailbox to fix and maxes out at a super low quota, so it’s useless for spamming.

That’s 100x better than the options on Office 365 which absolutely sucks ($$$) for low volume email coming from devices.

You can setup a receive connector on exchange online to trust mail from specified souce IP(s) (ie your onprem mailserver) with no need for additional mailbox licenses... good for alerting/reporting/MFP's etc

I'm curious, what are your thoughts on Zoho mail. You can use your custom domains even in their free tier

Zoho Mail's free tier doesn't include IMAP (for new accounts since about 3 years ago), so you wouldn't be able to use Thunderbird, FairEmail, K-9 Mail, or other third-party apps. Offline access on the free tier is restricted to Zoho Mail's desktop and mobile apps. Zoho's Mail Lite plan ($1/user/month) does include IMAP access, and you'll need to do some calculations to see whether Purelymail or Zoho Mail is cheaper.

https://purelymail.com/advancedpricing

https://www.zoho.com/mail/zohomail-pricing.html

It’s only 1 domain I think and they stripped out things like ActiveSync and IMAP a couple years ago IIRC. I use the $1/user/month plan and it’s decent. I don’t use calendars or contacts, so I’m not sure how that stacks up, but the email stuff is good.

The biggest annoyance is that someone used mx, mx2, mx3 for their MX instead of mx1, mx2, mx3, so the dns record indentation doesn’t line up. Lmao.

I've tried Zoho mail and the "problem" is that it's so much more than mail. It's a huge suite of online apps, really. That means if you purely need mail, it'll take a bit of time to find the setting you need.

(It's been three years since I tried it, and looking at my notes, I couldn't get Zoho to sync contacts for me, and somehow didn't get calendar notifications.)

I have a custom domain email address on Zoho and suffer constantly from delivery issues. Sometimes my emails go into spam filters, sometimes they go into a black hole. It’s a huge PITA and I am tempted to either move providers (maybe it’s Zoho’s fault) or just stop using my custom domain (maybe it’s not Zoho’s fault).

Well, I'm no expert and I'm not in any position to say anything negative about Zoho Mail... but the free tier you mention seems to allow for one domain. So it likely won't work if you have, say, 5 active domains you want to receive and send email.

I’ve used Zoho for a while and you can add on domains. It’s pretty cool and the online mail is a pretty decent UI.