catchall is an account that gets all emails that are targeted at inboxes that don't exist in the domain.
For example, let's say you have richard@domain.com and maverick@domain.com but someone sends an email to abc@domain.com
Since there's no inbox to deliver that email, it can go to a catch all account. It can also be discarded.
(I never used the email server of aaPanel actually, tho I may soon I have a customer who may come to use it)
