Can I use my iCloud+ custom email domain with third-party apps (IMAP/SMTP)?

Hi everyone,

I set up a custom domain with iCloud+ (let’s call it myname@mydomain.com) and it works fine in Apple Mail and on iCloud.com. I can send and receive messages without issue.

However, when I try to connect my iCloud account to a third-party mail integration (via IMAP/SMTP with an app-specific password), the only address that shows up as available is my @icloud.com address. My custom domain address (myname@mydomain.com) never appears as a “From” option.

I also tried authenticating directly with the custom domain address, but Apple’s servers reject the login.

Questions:

• Is this expected? Are custom iCloud+ domain addresses only supported inside Apple’s apps?

• Has anyone been able to use their custom domain address as the “From” identity in a third-party app that connects over IMAP/SMTP?

• If not, is this a limitation on Apple’s side, or am I missing a setup step?

Thanks in advance for any guidance!