You can’t merge two Apple ID accounts, those hubs of your iCloud, iTunes, and other Apple online identities. However, you can shift an email from one Apple ID to another if the email isn’t one issued by Apple.
This is often useful if you’re going to lose access to an email address—leaving a job, for instance—or if you were maintaining multiple accounts, and want to settle on just one. It can also be very useful if you had Apple IDs registered in different countries and want to migrate to a single one in a country you’ve settled into it.
There’s a set of warnings and limitations to consider, too:
