You connect iCloud Mail with an app-specific password from Apple. Your regular Apple password does not work here.
Step by step
- Sign in to your Apple Account: open your Apple Account.
- Choose Sign-In and Security and then App-Specific Passwords.
- Click Generate an app-specific password, give it a name you recognise and copy the code (four groups of four letters with hyphens).
- Open your profile, Email tab, click Connect account, enter your iCloud address and paste the code.
Two-factor authentication must be on for this; for most Apple Accounts it already is. If you change your Apple password later, all app-specific passwords stop working and you connect again with a new code.
Not working?
- Use your iCloud address (ending in @icloud.com, @me.com or @mac.com), not another address you sign in to Apple with.
- Still not working? Open Server settings in the window and enter only the part before the @ as the username.