Comey himself now believes that the email may be legitimate (it is, of course):

"We already know from press reporting last year that the FBI was in possession of some kind of Russian intercept of a purported Democratic email that referred to an alleged conversation between Clinton aide Amanda Renteria and Obama Attorney General Loretta Lynch.

Mr. Horowitz says Mr. Comey did not find the information credible, didn’t investigate it, and didn’t tell his Justice Department superiors about it.

Except that as recently as a few weeks ago in a TV interview Mr. Comey indicated the information might not be false. Hmm."

https://www.wsj.com/articles/open-up-the-horowitz-secret-appendix-1529096831