I’m currently with Google, and planning to move elsewhere. I have a Apple One subscription, and also a M365 home subscription (mind you, this might be something that I move away from over time, not sure I need the productivity tools in the future as the family isn’t using as much these days).
Currently, I’m using both Google and M365 backends (two different accounts for different purposes) as a bit of a test, just to spice things up I’m also using Apple Mail and Spark as my email clients.
Historically I’ve used Spark, as the auto organisation features are really quite good. I also like the overall design (iOS I better than MacOS), including a very satisfying swipe implementation (you can have short and long swipes, and the swipe distance is good, compared to Apple Mail where it often takes too much swiping…if that makes any sense at all).
I’ve tried Airmail (it’s just a bit clunky), Outlook (search is horrible, and the overall design is horrid) and a pile more apps that aren’t likely options for you due to the IMAP/POP block.
A few words about Spark
Spark can support EWS, so if your admin has set this up, might be worth a shot. If you are a SetApp user, it includes a premium subscription that seems to work with Spark giving you access to a few nice features (I also used the free version for years, it’s totally viable and still great experience). The snooze feature is the best in the business. AI stuff is ok I guess. I also like how it groups emails “slightly” in today / this week / last week etc in the left pane, not grouped, but just markers. It also makes the most of screen space overall, especially important on smaller devices.
Where Spark falls down, searching and e-mail composition (especially on mobile). Spark is great for actioning e-mail, keeping your overall inbox managed. However when it comes to finding stuff or trying to create complex emails with attachments, you will find it gets in the way a bit.
A few words about Apple mail
I’m finding myself trying to use Apple Mail more and more, given it is native, fully integrated and appears to be getting more and more love. The reminders integration is great (hey Siri remind me about this email, or use type to Siri) and the overall calendar and tasks from Apple are getting entirely usable. The new AI organisation features promise so much, hoping that with the next beta we’ll see them on iPadOS and MacOS, this could really sway my future direction. I love SmartFolders on MacOS, however can’t understand why these haven’t been added to iOS client. Overall Apple Mail is really well featured, however it takes quite a bit of discovery work to unlock them.
However on the flip side, the limited integrations (no action sheet for messages is just bonkers IMHO), no deeper integration between Mail/Calendars/Reminders is somewhat surprising. The free/busy time look-up works, but is a bit of a challenge, I find myself using web interfaces for meetings.
If you are mainly using email on MacOS devices, I’d go with Apple Mail. If you are more mobile and don’t need to send long heavy e-mail (mainly triage and light responses) I’d suggest giving Spark a go (assuming your admin allow EWS).
For me, I’ll see how the Apple Mail client ends up on MacOS and iPadOS, then make a decision. If I choose Apple Mail, I’d likely move my custom domain into Apple’s email infrastructure. If not, I’ll likely move from Google Mail to M365, mainly to stop Google poking about in my mail.
Good luck!