To receive and send emails from your own address (beyond 1-click Gmail/Outlook), configure IMAP and SMTP. Go to Settings → Inboxes → (email inbox) → Configuration.
IMAP (receiving)
Enable IMAP, then fill in: Server address, Port, Login, Password, SSL on, and the authentication mechanism.
Gmail example: server imap.gmail.com, port 993, SSL on, with an app password (not your usual password).
SMTP (sending)
Once IMAP is enabled, the SMTP section appears: Server address, Port, Login, Password, Domain, Encryption (SSL/TLS or STARTTLS).
Good to know: for Gmail, don't use the "Sign in with Google" button if OAuth isn't configured — use the manual IMAP/SMTP form with an app password.