The Mail Toolbar in Opera Mail
The mail toolbar comes with basic buttons, we will show you later how to add or remove buttons on the toolbar. This tutorial introduces you to the buttons and controls available in Opera Mail.
Below some commands, the equivalent keyboard shortcut is indicated. To create a new email within Opera, hold down the control key (Ctrl on Windows/Linux, or 
on a Mac), and then press E. For email labels, hit L and then a number, while the desired email is currently selected, and Opera Mail will apply the label.
Opera Mail's Basic Toolbar Buttons
Creates a new, blank email in Opera Mail, with focus in address field.
Ctrl+E Create new email
Creates a reply to the sender of the email currently selected
R Reply to current email
Creates a reply to the email currently selected, addressed both to the sender and all recipients of the original email.
Shift+R Reply to all (email sender and recipients)
Creates a forward of the selected email; if several emails are selected, only the last one to be selected will be forwarded.
F Forwards current email
Toggles the "Read" status of the email or emails currently selected.
K Marks the selected email(s) as Read
Shift+K Marks the selected email(s) as Unread
Toggles the Spam (junk) status of the selected email or emails. The button's image changes to a heart and envelope when focusing on an email already marked as spam.
Deletes the email(s) currently selected; in reality, it places them in the Trash view (folder) and stay there until you empty the Trash. The down arrow allows to expand a menu that lets you instead Remove [the selected email] from current view. (We will explain later what Views and Filters are.)
Del Delete selected emails
Ctrl+X Remove selected emails from current view
Expands into the Labels menu, which allows you to assign labels to the selected emails, or un-label them. (Available labels are Important, Todo, Mail Back, Call Back, Meeting, Funny, and Valuable.)
L, 1-7 Assign label to selected emails
L, L Un-label the selected emails
Creates a Contact filter for the sender of the email currently selected.
Assigns the email or emails currently selected to an existing filter, or lets you create a brand new filter. The Filter menu also allows you to extend the filter into a rule, (much more on that later).
Expands the View menu, which lets you customize the appearance of the current View, and toggle Quick Reply's visibility On or Off.
Sends all emails in your outbox, and checks the mail server for new emails.
F5 Check/Send
Checks on the mail server for any new emails to download.
Ctrl+K Check for new emails on server
Sends any emails you may have queued in your outbox.
Ctrl+Shift+K Send queued emails