The exact same thing happened to me when I was downloading a email containing a MIME base64 encoded PDF. I was curious as to what it was so I clicked the download button and Chrome warned me that it was malicious.

Funny, it doesn't give that same warning on this URL now. I've downloaded it and base64 decoded it but I'm slightly afraid to open it; I don't know how I'd do it safely. On a VM with no internet connection maybe?

https://wikileaks.org/dnc- emails/emailid/829

Space-broken URL provided above, if anyone wants it.