[toomuchtodo]

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)

[gasbag]

This seems like something we ought to be able to do electronically. I should be able to encrypt a message with recipient's pubkey and a verified timestamp from NIST (for example) in addition to my digital signature, with a requirement for decryption to result in a second call to NIST from the recipient and a record available to me of when it was decrypted.

[SomeStupidPoint]

If it's good enough to handle secret information, it's good enough for my official mail to corporations.

http://www.wrc.noaa.gov/wrso/security_guide/mailing.htm