I have (and don't know how I achieved this) an In box named All inboxes that holds all mail received in both my gmail and icloud accounts. I have tried to create a similar mailbox for all sent emails but can't work out how to achieve this. Tried creating such a mailbox and dragging the sent boxes from the two individual accounts onto it,but that doesn't work. Suggestions welcome.
'All Inboxes' is Mail's unified inbox – I don't think you needed to do anything to achieve that, I believe it is there by default.
There is an equivalent 'All Sent' mailbox.
To add this in macOS's Mail, hover over 'Favourites' at the top of the source list, and press the (circled) '+' button. In the resulting 'Add Favourite' dialog, select the 'All Sent' mailbox from the drop-down, and press 'OK'.
On iOS, press the 'Edit' button at the top of the mailboxes view, check the box next to 'All Sent', and press the 'Done' button at the top of the list.
Hi Andrew
I had already been given this information by Drew. Having previously ignored it I have now noticed that 'Favourites' sits quietly at the top of the list of mailboxes and the 'All Sent' mailbox is now set up. Thanks to both of you.
Michael Corgan 