In Vivaldi Mail, Outbox is a sub-folder in All Messages, where you can store message drafts that you’ve finished writing, but don’t want to send just yet.

To queue emails instead of sending:

1. In the Mail Composer, click the little arrow (▼) next to the “Send” button.
2. Select “Queue”.
3. When you’re done writing an email click the “Queue” button (previously “Send”).

To send all emails in the Outbox.

1. Open the Mail Panel.
2. Click “Send from all accounts” at the top of the panel.