All three are set in cPanel under Email, and none of them counts as a mailbox.
Forwarder — copies mail sent to one address on to another (or several). Email → Forwarders → Add Forwarder. Use it for info@ going to two people, or an old address that should reach a new one. A forwarder can exist without a mailbox behind it, so sales@yourdomain.co.uk can simply forward to jane@yourdomain.co.uk.
Alias — in cPanel terms this is just a forwarder to your own mailbox. Sending as the alias is done in webmail or your mail app by adding it as an identity/"send as" address.
Catch-all — receives anything sent to your domain that doesn't match an existing address (typos, old staff addresses). Email → Default Address → Forward to email address. Worth having for a small business, though expect it to collect more spam than a normal mailbox.
Two cautions. Forwarding to Gmail, Outlook.com or similar can land the forwarded mail in their spam folders, because it arrives "from" the original sender via our server — a mailbox here checked directly by IMAP avoids that entirely. And a forwarder to an address that bounces will bounce back to the original sender, so check the destination exists.
