Few notes
- iOS issue stems from a recent upgrade from an iframe to a webview. It's fixed on all mobile apps and versions.
- All DMARC-failing mail does go to spam.
- Caching images on receipt was examined but deemed impractical. It balloons email size from generally 50-150 KB to possibly multiple MB. Even for a personal mailbox, this could lead to 100s of GB being stored. Some version of this could be done on device or in the browser and temporarily stored. I actually think iOS either does this or will do this in the future.