Microsoft's on and off relationship with linked inboxes in its Outlook Mail app for Windows 10 Mobile is apparently back off again. The feature, which was available in Windows Phone 8.1, but then initially disappeared in early Windows 10 Mobile builds, eventually made it back into the app in recent builds. However, with a release of the Outlook Mail and Calendar apps to go along with the "final" version of the operating system, the apps had some stability issues, ie: they crashed, which apparently was caused by the linked inboxes feature.
Microsoft has issued a newly updated set of apps that fix the crashing, but by removing linked inboxes. Hopefully, we'll see the much requested feature back again soon, but for now it's probably better to have an app that doesn't crash than a feature you can't use anyway.
We'll keep you posted on if and when linked inboxes show up again, hopefully to stay. In the meantime, if your phone hasn't already updated, you can get the latest app from the link below
Via Windows Central