Mailcast is supposed to be simpler than usual newsletter software (there are no advanced marketing features) and it is self contained (no need to integrate with a MTA server or service). It can be used with large lists but it is not supposed be used like this if you do not want to spend a lot of time solving deliverability issues (sending to smaller lists is much easier to manage than large lists)
Screenshots: https://cloudup.com/cpNpzlf3V5j