Currently, we do not generate user emails; instead, they are provided by the HR auhoritative source.
We have the following requirement: If a user’s email changes, HR will send an update to ISC, and we must update the email in Active Directory by modifying the mail attribute and proxyAddresses(The old email should be kept as an alias, while the new email should be set as the primary email)
Enable Attribute sync for email and Proxy Address as well
Proxy Address is a multi-valued attribute, you can generate the values as comma separated and can be converted to list at provisioning side using cloudDelimiter attribute in AD provisioning form.
Check whether latest email is there are not in current proxy list if not then update the value.