After the recent spread of WannaCrypt, there has been a lot of warnings about the dangers of emails and clicking on links in them.
But the malware is spreading as a worm using SMB to infect other vulnerable computers.
Here is Microsoft's answer to the problem:
Customer Guidance for WannaCrypt attacks (Microsoft Technet, May 2017)
you'll notice they have no mention about emails in there.
My question is in the title: What do emails have to do with the spread of WannaCrypt?