- Open Spark → Settings → Accounts, and select the account you want to send protected attachments from.
- Find the Outgoing Server (SMTP) section — for accounts added as a custom IMAP account, this is directly editable; for Google or Microsoft accounts added via their own sign-in, see the note below first.
- Enter the gateway's inbound server settings — server address, port, and your account email as the username.
- Match the connection security to your port (SSL/TLS for 465, STARTTLS for 587), save, and send a test message.
Spark signs Google and Microsoft accounts in via OAuth by default, which doesn't
expose a custom SMTP server field the way a plain IMAP account does — if your
account was added that way, check whether Spark offers an "Advanced" or "Custom
server" option during setup, or add the account as a generic IMAP/SMTP account
instead so these fields are available.