A catch-all refers to a mailbox on a domain that will receive all the emails sent to inexistant accounts on that server.
While configuring a catch-all email address can help to avoid losing important emails due to misspelling or typos, this feature is sometimes forbidden in email hosting providers because help spammers to abuse the feature.
If an email address firstname.lastname@example.org is configured as the catch-all email address on example.com, then all emails sent to undefined accounts on that server will be received under email@example.com – The sender won’t receive a rejection notice or Undeliverable message.
Of course this has some pros and drawbacks.
With the increase in spamming, it is a better practice to reject all unknown email addresses. This helps to combat spam and reduce network traffic. Instead of a catch-all, email addresses that could cause confusion can be configured with an alias.
EmailVerify can help to analyze email addresses and determine if the email address is valid or not. Internally, it uses a proprietary technique to determine if a server has catch-all feature enabled.