Catch all email accounts are accounts that will accept mail from any account name that does not exist on the server.

The "Pre-SPAM" era benefits to having a catch all account were that no mail would go undelivered to a domain mail account regardless of any mistakes made in addressing the username. For example, if you intended to send mail to support@lhhosting.com and instead you spelled support wrong (suport@lhhosting.com) the mail would end up being delivered to the catch all account at lhhosting.com.

Catch all accounts became obsolete with as the SPAM email systems began mass mailing with "dictionary attacks". Dictionary attacks refer to email addressed to some of the most common email addresses in the dictionary. For example, most SPAM would be sent out to common first names (bob, joe, sue, etc.,) in the hope of finding valid email accounts at a specific domain. Also, they would send out standard emails to support, help, admin, webmaster and so on for any given domain in the hopes to catch a vaild email account.

Based on the dictionary attack type mass mailing if you had a catch all account then none of the email would get rejected. You could receive thousands of pieces of email in that account from one single attack.

Even if the end user didn't care about the bogus mail we do. It would add a large overhead to our bandwidth allocations for mail just for a single SPAM delivery.

For these reasons catch all accounts are prohibited on our mail systems.