- In Outlook, tap your profile picture → Add Account → Add Email Account.
- Enter the email address you send protected attachments from. If Outlook offers to sign you in via Google or Microsoft directly, choose to add it as an IMAP account instead — that's the only account type that exposes a custom outgoing server.
- On the account setup screen, enter the gateway's inbound server settings as the Outgoing mail 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.
Accounts signed in through Outlook's own Google/Microsoft OAuth flow don't expose
a custom outgoing server — this only applies to accounts added as plain IMAP.