Best iOS email app for a Guard-encrypted mailbox? (switching from Android / K-9 Mail)

Hi everyone,

I'm moving from Android to an iPhone and trying to figure out the cleanest setup for reading my mail on iOS. I have mailbox Guard active with the encrypted mailbox option turned on, so every incoming message is stored PGP-encrypted (PGP/MIME) on the server.

On Android I used K-9 Mail together with OpenKeychain, which decrypted everything automatically in the inbox using my private key on the device. That worked perfectly. The problem is that iOS doesn't allow PGP plugins in Apple Mail, so I can't just replicate that setup.

Because the whole mailbox is encrypted at rest, manual per-message tools (decrypt-by-share-sheet utilities like iPGMail or PGPro) aren't practical — I'd have to decrypt every single email by hand. I really need a native client that imports my private key and decrypts PGP/MIME automatically as it fetches over IMAP.

A few questions for those of you already running Guard on an iPhone:

1. Which iOS email app do you actually use day to day? Does it auto-decrypt PGP/MIME from a Guard-encrypted inbox without manual steps?
2. Canary Mail seems to be the main native option with built-in OpenPGP. Does it handle Guard's PGP/MIME reliably? Any gotchas with key import or signing?
3. Is there any open-source iOS client that works, or is closed-source the only realistic route on iOS right now?
4. For the privacy-minded: do some of you just skip a native app entirely and read through the web client (server-side decryption with the Guard password, private key never leaves the server)? How's that as a daily driver via a home-screen shortcut?
5. Any concerns/experience with importing the Guard private key into a closed-source app on a phone?

Basically I'm weighing convenience (native app, key on device) vs. keeping the private key off the device (webmail). Curious what trade-off the community landed on.

Thanks in advance for any pointers!