Missing Authenticated Domains page or Page Not Found Error when setting up Authenticated Domains for Marketing Cloud

To resolve the above issue, navigate to the Migration page in Salesforce Setup (under Unified Messaging → Email → Migration).

Clicking the Transfer button on the Migration page will trigger a change in your Salesforce org that allows admins to configure a custom authenticated domain for email sending. Please note this authenticated domain feature is only available to orgs with Marketing Cloud (Growth/Advanced) or relevant Marketing Cloud Account Engagement editions. Authenticated domains for sending marketing emails is not available for the Marketing App in Salesforce Starter, Salesforce Pro Suite, or Salesforce Foundations.

The Migration page will show a status indicator, Pause or Complete All Campaigns, that is a pre-requisite before clicking Transfer.

• Pausing campaigns will have to be completed manually, the transfer button itself won't pause any campaigns automatically. This only applicable if you previously sent emails from campaigns in Salesforce using the Marketing App (with Salesforce Starter, Salesforce Pro Suite, or Salesforce Foundations). 
• The status indicator here will be green if the system detects that there are no campaigns that need to be paused or users have already paused any relevant campaigns that have an email action that would be potentially impacted by the transfer.
• If the status indicator is green, you can proceed safely with the Transfer. 
• The only campaigns the system checks are ones that are used with the Marketing App to send marketing email.

Please note that this Transfer button has no impact on any domains used in any other Marketing Cloud product or any external system.

• You will still need to set up authenticated domains for Marketing Cloud afterwards.
• The Transfer button will allow you to start setting up authenticated domains but will not automatically trigger creation or setup of these domains. You will still need to configure DNS records with your IT team to authenticate domains with Marketing Cloud.
• You may need to wait some time (up to 24 hours) after clicking Transfer before the Authenticated Domains page becomes visible in Salesforce Setup.

For Marketing Cloud Account Engagement customers:

• This Transfer button has no impact on any of your Account Engagement campaigns, automations, email sending, etc.
• It does not impact your currently configured Account Engagement sending domains in any way. 
• This only impacts your Marketing Cloud Next setup and is a required step for moving forward with Marketing Cloud Next setup.

Important Notes

• This Migration cannot be undone. After Migration, emails sent via Marketing Cloud Next will consume Salesforce Message Credits.
• If you are an Account Engagement customer, you must purchase the Salesforce Message Credits - Email add-on from your Account Executive prior to proceeding with the Migration to ensure that your email sending via Marketing Cloud Next is not impacted.