Opera Mail - our built-in email client - helps you fill in email addresses automatically as you type. This auto-complete feature is based on your contact list, Opera's built-in address book.
When replying to a message from an unknown email address, Opera assumes you know the person you are replying to, and automatically adds their email address to your contact list, so you can use it next time.
For more about Opera Mail, see Opera Help — Email and news.
Need help? Hit F1 anytime while using Opera to access our online help files, or go here.