I'm not getting verification codes on my mailbox.org alias

I tried to change my discord email to one of my mailbox.org aliases and I'm just not getting it in my inbox. I checked the junk folder and it's not there either. What's going on? I just signed up for this today and I don't know very much about email providers other than Google and Apple. I filed a support ticket, but I'm not sure when they'll be able to get to me. Does anybody know what's happening?