I have 2 email accounts (one personal and one for my work/main project). Currently I need to manually switch the inboxes. It would be great if there would be a simple "Unified inbox" which lists all emails from all inboxes together in one stream.
How would you like it to work?
As the first entry in the left navigation there could be "All inboxes", which could also be the entry opened by default (unless you want to remember the last open inbox). To distinguish different accounts, color coding in the row would be possible.
Relevant links, screenshots, etc
The screenshot is slightly outdated, but in Nextcloud Mail we do it like I described. The color coding is done by a bar on the left of the messages in the list, but in practice I don't even really look at it:
Other email apps (like AOSP Mail, K9-Mail and others on Android) do it similarly.