If a website with the Newsletter modules is hosted outside Plako, the whole automatic return treatment system will not be available.
The sending system is also different, once it'll not be sent by an external system (as happens in Plako's servers).
Some functionalities will not be available, such as the attribution of credits to clients through the "Client Area" of the partner; this means it will not be possible do limit (or manage) how many Kb each client has available for sending newsletters.