You can't sign in to with an email alias.

You can change or delete an email alias, but if you delete an or email alias, you can't add it back to your iCloud account.

If you created one or more email aliases for your account, be aware of the following: In each case, you can sign in to iCloud with either your email address or the Apple ID that you use with your iCloud account.

If you had a working email address as of July 9, 2008, kept your MobileMe account active, and moved to iCloud before August 1, 2012, you can use and email addresses with your iCloud account. Out of the 3 huge providers of email (icloud, gmail and outlook) which would you choose today, if could get a do-over (you dont have to tell friends/family/etc.

If you created an iCloud account before September 19, 2012, or moved to iCloud with an active MobileMe account before August 1, 2012, you have both and email addresses.

If you created an iCloud account on or after September 19, 2012, your email address ends with Learn more about mail addresses.

It can be used with the Mail app on your Mac computer or iOS device or using MS Outlook on a computer. Review these scenarios to see which one applies to you: iCloud Mail is an email service operated by Apple.

Icloud mail vs gmail