[CM30]

Perhaps it's from someone they were investigating for other crimes. I mean, it doesn't seem beyond the realm of possibility that law enforcement were going after say, a drug dealer who was using the site to sell goods, and found the welcome email from the platform he or she was using in their inbox.

That seems like one plausible possibility.

[ATsch]

This is my pet theory. A seller was busted and the emails were siezed. Seems like the most likely possibility.