icloud emails not forwarding consistently

Hey there ivankboardley,

Thanks for asking about iCloud email and the forward feature.

Sometimes all it takes it to turn this setting off, restart your involved devices, and then go back and set it up again: Automatically forward email in Mail on iCloud.com - Apple Support

If you still have issues after those steps, we'd like to help by learning more about what's happening, along with ruling out some general possible causes:

1. You mentioned that all of your iCloud Mail was being forwarded to a different account up until recently, but when did this start to first occur?
2. What messages exactly are not getting sent? Can you isolate it to one provider, or one contact, or during a time when iCloud was experiencing an outage?
3. Check for outages now and in the future, as iCloud can't forward emails during those times: Apple - Support - System Status
4. While we do not need to know the full email address to which you're forwarding your iCloud Mail, who's the email service provider to which you're wanting to forward those iCloud Mail messages?
5. Which device are you using with iCloud Mail, and have you already tried any steps(like a restart for example)?
6. Are your devices all updated?

Shut down or restart your Mac - Apple Support

Restart your iPhone - Apple Support

Restart your iPad - Apple Support

Update macOS on Mac - Apple Support

Update your iPhone or iPad - Apple Support

Cheers!