The catch-all facility for emails basically 'catches all' emails addressed to a domain that do not exist on the mail server. It avoids losing mails due to misspelt or mistyped email addresses.
For example we may have a catch-all set up as support@nuttyabouthosting. Then if someone was to email firstname.lastname@example.org (we have no Bob working here at present!) then it would be delivered to support@ rather than being rejected as 'undeliverable' or 'unknown user'. Similarly if someone sent an email to support@ it would get to it's destination.
All sounds good? However we, like many hosts, do not offer this facility as it is often abused by spammers causing problems for everyone on the mail server. Mass spamming can mean mailboxes full up quickly and if users then forward emails to another external email address then the IP address the mail server is on can be tarnished or even blacklisted.
The best practise is to create email aliases and we have no restrictions on the number of email aliases you can create. For example support@ or support.staff@