You must have an @icloud.com, @mac.com or @me.com address to login as an iCloud account. If you use an Apple ID, which is not an Apple email address, you can do one of two things. Login using another Apple email address as an iCloud account or Login using the other credentials as that type of account. Then within Swingmail you can link all your other email addresses together.
You can create @icloud.com addresses here
You can check your email addresses linked to your Apple ID as follows.
Go to https://appleid.apple.com and login.
Choose your account.
1. The address here is your Apple ID address.
If it is not @icloud.com, @mac.com or @me.com then you can not login to Swingmail as an iCloud account with this address.
2. Instead choose another of your email addresses ending in @icloud.com, @mac.com or @me.com and login with that.
you need an app specific password in order to login to Swingmail. You can generate one by going to https://appleid.apple.com logging in.
Go to Security.
Select App specific password.
Enter the Label.
Use this app specific password to login to Swingmail with your @icloud.com, @mac.com or @me.com address.