Dunno but I don't imagine why not. If they are looking for bank fraud, and considering that all of Trump's business, and therefore Cohen's (Trump being his only client) pretty much filters through Russia (this is known and long-admitted to by
Tweedle dickless), then I think if you are looking at specific bank transactions--apparently in this case, maybe involving a donation from a Ukrainian steel magnate--then any type of email related to that would be relevant. Who knows what else is in those specific emails, but I think the warrant is strict about the manner in which and type of evidence that can be gathered. I would think that once those barriers are satisfied, then all of the information within that evidence becomes open for investigation.