Opera mail folders
I have recently switched to Opera Mail and I think it is the best email client by far. As an entrenched Outlook user the transition was seamless and I love it more and more as I get used to it.
I have tried every mail client out there and nothing compares.
However there is 1 feature in "Mailbird" that is a winner. This is the small button on the edge of the page that allows you to move or tag an email with the folder name. This also shows up at the top of the email.
I know you are using labels and these work really great but when you have thousands of emails that need to be sorted it makes sense to use the folders as this is how they are sorted on the server.
If you can do something like this then "I" believe that you will have the best of the best!!!!
You're using IMAP, correct? The way you do it in Opera is to use the email@example.com IMAP folder access point for the account in the mail panel. You drag the message (or selection) from the IMAP folder it's in to the IMAP folder you want to move it to. If you want to copy instead of move, you ctrl + drag.
But, you can use cut/copy and paste (via the right-click on message/selection or ctrl + x / ctrl + c and ctrl + v) to do the same.
It basically works how you copy/move files in Windows Explorer. Note though that when moving a file from an IMAP folder in one account to an IMAP folder in another account, Opera will force a copy action instead of a move (causing you to have to delete the original if you actually want to move).
There's no move to / copy to option option though and no button for it. Try using dragging or the keyboard shortcuts for a while to see if you like it.
If you're going to be working for IMAP folders, you can drag the firstname.lastname@example.org IMAP folder access point to the top of the mail panel and use that list and ignore the All Messages access point etc. It's up to you.