Hello there,
If you have an on-premises Active Directory Domain Services (AD DS) environment and you want to join your AD DS domain-joined computers to Azure AD, you can accomplish this task by doing hybrid Azure AD join.
In a hybrid deployment, digital certificates are an important part of securing the communication between the on-premises Exchange organization and Microsoft 365 or Office 365. Certificates enable each Exchange organization to trust the identity of another. Certificates also help to ensure that each Exchange organization is communicating to the right source.
Certificate requirements for hybrid deployments https://learn.microsoft.com/en-us/exchange/certificate-requirements
Plan your hybrid Azure Active Directory join implementation https://learn.microsoft.com/en-us/azure/active-directory/devices/hybrid-azuread-join-plan
Hope this resolves your Query !!
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