Rather than sending an email to verify a trusted device, why not offer an option to send a text with an authorization code.
Scenario; My wife needed to access our insurance account with her phone. Last Pass refused to open, without an authorization email. She uses last Pass on her phone, but she is not at home, so it "became - not a trusted device". She can't access email without access to Last Pass. She calls me at work, I have to log-in to email from my desktop browser and authorize her device. I have had this happen to me as well. If we were both away from home or work, there is no way to access email on a "trusted device". I have had to turn off the security on "Trusted Devices" because we can't trust Last Pass to know it is a "Trusted Device".