- In Outlook, tap the menu icon → your account icon → Add Account → Add Email Account.
- Enter the email address you send protected attachments from, and choose to add it as an IMAP account rather than signing in through Google or Microsoft directly — only a plain IMAP account exposes a custom outgoing server.
- On the account setup screen, enter the gateway's inbound server settings as the SMTP server, along with the matching port.
- Enter your account email as the username and your mailbox password, then finish setup.
- Send a test message from this account to confirm it goes through the gateway.
As on iOS, an account signed in through Outlook's own Google/Microsoft sign-in flow
doesn't expose a custom outgoing server — add the account as plain IMAP instead if
these fields aren't available.