Using custom subdomains for each account is a great idea. Once you start getting spam on this subdomain, you just need to remove the DNS entry and the spammer's

Using custom subdomains for each account is a great idea. Once you start getting spam on this subdomain, you just need to remove the DNS entry and the spammer's attempts to deliver spam will be unsuccessful (versus if you use different local part names, you have to filter / reject the mails explicitly).