I once had a chat with a security professor who had decided to try to get his group to use encrypted email for all of their communications. And they just couldn't get mailing lists working right with encrypted email.
Thus, participants are pooled under 1 time constrained key exchange, participants sections origins are signed/time-stamped, and the ciphertext expires on a schedule.
Why? so at some future time side-channel key exfiltration can't be used to data mine the entire history of past tapped conversations/ciphertext. Even if a private signing key is stolen, it is difficult to rebuild the lost ephemeral key session.
Have a nice day. =3
Depends what you do, and if your organization has a persistent clown infestation. Some big business folks still use email as a human to API interface.
Running out-of-band public keychains is not something most people will ever need. =3