Yes, I think this is legit! Adobe Marketo Engage subscriptions require all non-API users, including Marketo Engage Administrators, to verify their email addresses. Single Sign-on (SSO) users who are not assigned an Admin role, or who are assigned a role with the ‘Bypass SSO’ permission, will automatically have their email verified when their subscription is enabled with the Email Verification feature. Check out the full Email Verification requirement documentation on experience league here. This documentation page also has a snapshot of verification email that Adobe is sending.