On your Mac, you may get an error message that says "The account already exists" when you try to add an email to your Apple email either on your iPhone or on your Mac. You may also get a similar error message saying 'this imap account has already been added' on your iPhone or 'an smtp account already exists. only a single smtp account is allowed to save'.
Apple: Mac Mail – Account already exists error when adding Gmail (14 solutions!!)
Your iPhone or Mac is trying to tell you that this account is already in your iCloud. This problem can be really frustrating especially when you are trying to use your Apple email, so below are fixes that can help you get rid of this error.
You're seeing the "Account already exists" error because there's a problem with iCloud Keychain. iCloud Keychain syncs a lot of data across your Apple device—the email you're trying to add is among your iCloud data trying to sync, but it's stuck. When you sign out of iCloud, the email in Keychain stops syncing, so you can add the email to your Apple Mail.
If the error still persists after signing out, there may be a bug on your iPhone or Mac that is causing the error to still appear. You need to troubleshoot the problem to get rid of this error.
