I also use Killer Contract, slightly tweaked of course. It's simple, understandable and gives me some leverage when clients don't pay, which happens a lot more often that i would like.
Setting up my own mail server a couple years ago i had this problem. The "best" solution seemed to be routing through a service like gmail, which defeated the purpose.
Many airlines also wont allow shipments of lithium or things containing lithium batteries on passenger flights. Apparently they have a habit of spontaneous combustion. So shipments of iphones have to be specially packaged and sent on cargo flights.
Just my opinion but, HN isn’t Reddit. That's a good thing. There are extensions/etc. that handle notifications. Perhaps in the spirit of HN wullwong should 'hack' it. Make a plugin or service to do this and show us what they created to make notifications easier.