The groups also argue that a Fourth Amendment “moment” doesn’t occur when someone views the emails, as the government has argued, but instead when those emails are collected. Here’s the EFF explaining the position outlined in its amicus brief, from the same blog post:
The Fourth Amendment event [occurs] when Microsoft copies the emails to turn over to the government. That moment is a Fourth Amendment ‘seizure’ since at that point, there is a meaningful interference with the email user’s right to possess and ultimately control his messages. In other words, once these emails are copied, the user loses the ability to decide who gets the messages and for what purposes. A contrary decision has serious privacy implications as it allows the government to adopt a ‘seize first, search later’ view of the Fourth Amendment, where the government can seize a computer, copy all of its data, and keep that information indefinitely—without a search warrant at all.