Sending correspondence certified mail, return receipt [1] is standard practice for creating a paper trail [2]. There is no such thing with email.

[1] https://www.wikihow.com/Send-Certified-Mail-(USA)

[2] http://www.kalzumeus.com/2017/09/09/identity-theft-credit-re...

Control-F "Do you like paper trails? I like paper trails. I particularly like paper trails where the United States Federal Government attests to the exact minute your firm learned the contents of this letter." (hat tip to patio11)