Sending Mail via SMTP Does not Trigger Bounce Notification

I am sending emails via Golang and SMTP (iCloud with port 587 and host smtp.mail.me.com), however when I send to a clearly existent email address such as jkahsdfaksjhdl@kjhasdfkljhasdlkjhf.com, I do not get a bounce notification from iCloud.

The message is properly showing in my sent folder as well. We are also including the Return-Path header.

However when I send the exact same message via the UI, I do get a bounce notification. Is this intended functionality?

Thanks and let me know!