[Weethet]

FastMail is using JMAP, a protocol designed to support push notifications. MXRoute is stuck with SMTP/IMAP which don't support those. There might be a different reason, but I think this is probably the core issue here

[jarland]

The stock iOS Mail app does not support JMAP and therefore it has no relation to Push notifications for the stock iOS Mail app.

[admdly]

I think saying they are stuck with standard email protocols is a bit of a stretch. JMAP is not widely implemented outside of Fastmail and certainly isn’t used by Apple Mail, which actually uses a proprietary IMAP extension (XAPPLEPUSHSERVICE).