As many addresses/aliases as you want on as many domains as you want. Custom filtering/sorting. Easy burner addresses. Custom reader tracking for marketing.

As many addresses/aliases as you want on as many domains as you want. Custom filtering/sorting. Easy burner addresses. Custom reader tracking for marketing. Custom reader db response pattern mailouts/campaigns. Some of these are Some Assembly Required, but they're hard/impossible/expensive to do with 3rd party mailers.