Don't want to change corporate apple id

So follow the link in that email and change the primary email address for that AppleID as instructed. You can use any other email address you have that is not in use already as an AppleID. If you need an email address get a free gmail, yahoo or whatever account to use.

Since the company owns that email domain, they are within their rights insisting Apple not allow them to be used as ApppleIDs if they wish to. It sounds like they are adopting a policy of no longer allowing company devices to use personal AppleIDs. Are they going to a managed deployment of devices instead?

I know the company I work for does the same. If I tried to use my company domain email address as an AppleID, the email server would block receipt of the verification email.

Unless the company also has your Apple ID password, they won't have any access to your iCloud data. The problem you might run into is if you need to reset the account, you'll have no access to the primary email address.

Why do you want to keep the company email address as your Apple ID. Perhaps if you could explain why, someone could provide additional advice.

It is dead easy to change the email address you use for your Apple ID. You lose not data or access.

Ok, that makes more sense. You should definitely provide the company with the password before you leave so that they can reuse the phone.

There are certainly people who have one Apple ID for a personal phone an a different one for work. I misunderstood and thought you meant you were leaving the company but didn't want to change your Apple ID. What you're doing sounds fine.

Given the email you posted above, it appears you don't have a choice. Apple may refuse to recognize the ID and permanently disable it since you are using an email address that your company and you no longer have the legal right to use.