Looking for opinions / insights. I responded to a proposal on UpWork where the client needed four emails - four built for desktop and four built for mobile. I responded that in my experience responsive emails are the route to go. The proposer responded:

"we have spent 20 years doing email marketing and to us seperate mobile designs are a must in this day and age. We don't believe in responsive. Thats the lazy way out."

I responded that I would be open to understanding their process.

Is this true? Should we now be designing two separate emails for desktop and mobile? If so, do all ESPs have the capability to serve the correct version to the end user?