@MostlyHarmless welcome onboard!
Just to double check , you are referring to the email from your Cloudron dashboard at my.domain.com, right ? (i.e not some email from cloudron.io) .
Cloudron is entirely selfhosted. So, for my.domain , email is sent from your server (and not via our servers). It's quite common that your VPS provider blocks this. First step, is to check email status - https://docs.cloudron.io/email/#server-status . Is it all green?
Are you able to send a test email via https://docs.cloudron.io/email/#send-test-email ?
Check the mail server event log - https://docs.cloudron.io/email/#event-log