From CNN:

The newly discovered emails are part of an investigation into Anthony Weiner, according to law enforcement sources. Weiner, the disgraced former congressman, recently separated from top Clinton aide Huma Abedin after a sexting incident.
The FBI and the New York Police Department have opened preliminary investigations of allegations that Weiner, a former New York Democratic congressman, exchanged sexually explicit text messages with a purportedly underage girl.
The emails in question were sent or received by Abedin, according to a law enforcement official. There were a "considerable number" of emails being reviewed from at least one device shared by Abedin and Weiner, the official said. A separate official described it as thousands of messages.
The FBI is looking at whether any of the newly discovered emails will have an impact on the now-closed investigation into Clinton's server. In his letter, Comey said he was not sure how long the additional review would take and said the FBI "cannot yet assess whether or not this material may be significant."

What I'm getting out of all this is that 1) Weiner is not only toxic, but contagious as well, and 2) The Trumpers are trying WAY too hard. Desperation.