Once a message is deleted and in the trash there’s no way to restore it back to it’s corresponding inbox folder…
You can move the message back, just like you can move the message between folders. In version 5.7xx, it’s in the 3-dot menu » Organize » Move.
Thanks for your answer but there’s no such possibiliy.
Running 6.711
No restoring, no “organize” 
The answer you reference is over two years old and menu entries might have changed.
Go to Trash folder, select mail(s) you want to undelete, select 3dot menue, select “Move”
Only options are “add star” and “select all”…
And the “delete” and “mark unread” besides the three dots.
Are you using POP3 to connect to the server? POP3 does not support moving messages between folders (actually, POP3 does not really support folders at all)
POP3.
And any other email program has no problem in doing so.
…nobody else finds it rather strange that you can’t recover emails.from the trash folder…?
I have had the same experience and am of the same opinion.
2 Likes
+1
The three dots only show me mark as important and select all, but no move or undelete.
I am also using POP. The folder feature is provided thru k9mail and not via the server.