Lawyers are heavily reliant on emails, and often assume the authenticity of emails.
Unfortunately, emails can be easily forged, unless certain precautions are taken.
Those records enable the recipient of an email to know how to verify if an email which claims to have come from your firm actually was authorised to come from your firm.
Without such records, your recipients cannot verify whether or not your communications have come from you, and they will not know to reject the forged emails.
A good way to see whether your firm is publishing these records is to send an email to firstname.lastname@example.org.