I just tried changing my email on studentaid.gov to a simplelogin alias (using SL is a habit at this point) and I got notifications that emails from it were bounced while trying to verify the email change with sent codes. I looked it up and found a bunch of Reddit posts about issues with SL and iCloud.
No I did end up changing my studentaid email to an SL alias, though I might wanna change it back if it keeps having issues. The issue is that icloud bounced the email, and SimpleLogin itself gave me an email each time one got bounced, with to go to simplelogin.com and see the bounced email. This is the title for each one