Gmail – Keyboard shortcut to change Right-to-left status in Gmail

To label the currently open mail, press L and start typing the label. Matching labels will appear as you type, so you can just navigate to the one you want (using arrow keys) and press Enter.

To label AND archive the mail at the same time, press V instead of L and follow the same procedure.

In the mail list view, use J and K to move up and down the list (the tiny arrow to the left of each item will move), press X to select one or more mails and then use L or V to add labels.

esc + o + a

esc : gets you out of edit mode

o : opens the document [basically returns the document to 'unedit' state.

a : reply all