You begin the invitation process by browsing to premium.outlook.com and signing in with your Outlook.com Premium account.
This is your Outlook.com Premium Account Domain Dashboard.
Click/Tap Invite Others to begin the invitation process.
Provide the requested information and then click/tap Send Invite.
You will be returned to the Domain Dashboard where you can exit or click/tap the Invite Others button to invite additional guests to use your custom domain.
Your invited guest will receive this email from Outlook.com Premium and just needs to click/tap the Accept button at the bottom to begin the sign-up process.
They will then be sent to the Outlook.com Premium home page and they just need to click/tap Sign in to get Started.
They will then be taken to this page where they pick their e-mail address on your custom domain. They will need to click/tap Check Availability to continue.
They will then see this confirmation that their requested e-mail account is available and then can choose to make it the default from address for any e-mails they send that that account.
If they click/tap No then the process of choosing an e-mail address will start over.
Once they have accepted their new e-mail account options they will be returned to their Domain Dashboard.
From there they can go straight to the inbox or they can click/tap Advanced Settings to select aliases for this account using the custom domain.
Alias account management page.
Once they have signed-up there will be another e-mail from the Outlook.com Premium team with more details and links to information about how their new account works.