Both protocol availability and support in widely deployed messengers will be necessary. Key/identity management will need to pass regulatory/legal scrutiny, but once we have interoperable, multi-vendor encrypted messaging that is usable by mere mortals and globally available at low cost, various groups can start lobbying for regulations that encourage migration to MLS-enabled communication.

The other issue with digital messaging is endpoint security and message archives, after the message has been transported. A pile of faxes is not easily accessed remotely, unlike a disk with message archives.