At the beginning, we see Neil's sister barge into his room, type in 4 people to forward the chain email to. We see Neil add a 5th name. Technically, he sent the letter to 5 people. So why does he still die in the end? I'm confused.
True, but the killer waiting until each person deletes the message leads me to believe that he's killing at random. After all, he can't plan who the message is forwarded to. But, the killer then repeatedly sends Neil the chain letter, at which point Neil has to repeatedly send the chain letter onto five more people, which indicates that Neil, and by extension Neil's friends are being targeted. It's a plot hole because it can't be both ways. It's one or the other. The movie fails to follow the logic it sets up.
The way I took it was that the killer somehow knew that Rachael had started the email forwarding and counted it against him? Or maybe, just maybe, he really hated how into technology Neil was (we did see him doing way more online than any of the other characters).