These are legacy Apple email addresses brought from the past. If you established them at the time with the same Apple ID you are now using they are part of your account.
Read iCloud: About your @icloud.com, @me.com, and @mac.com email addresses - Apple Support which explains their status.
When Apple updated their various cloud services the old addresses were added as aliases to the new form of email, so @mac.com is part of @icloud.com today.
Apple notes in the document I've linked that You can change or delete an email alias, but if you delete an @mac.com or @me.com email alias, you can't add it back to your iCloud account.
You can delete them by signing into your iCloud account on the web and going into the Mail tab and from there clicking on the preferences clog (top left), then Accounts. From there you will see the alias options. I think you can also do it in Mail on a Mac but I'm not going to test this. I'll let you have a go: Mail > Preferences > Accounts > iCloud > Account Information> Email Address > Edit Email Addresses