The way I do it is I use a subdomain for any aliased email, e.g. vendor.com@account.mydomain.com and then I just have rules to move anything sent to account.myd

The way I do it is I use a subdomain for any aliased email, e.g. vendor.com@account.mydomain.com and then I just have rules to move anything sent to account.mydomain.com to a separate folder, then it never shows up in the main mailbox unless I put it there myself. Works fine!