I did some research on this last week and forgot to reply. It appears that yes, you are right, that it was never possible to get digests even when active on the site. With best of intentions, @BhaelOchon sent me on a wild goose chase. 
What would it take to add a feature to allow digest delivery for active users? My globally dispersed, email centric community is feeling the weight of information overload. People are tuning out discourse and are ignoring the important notifications about topics they are mentioned in or involved in. When they do log in they ignore the notifications bubble and feel lost. This despite repeated reminders directly and through documentation on the forum.
Providing an email digest of latest activity would go a long way to coaxing these people into our new, discourse way of doing things. As my colleague wrote, she needs a reminder email and a āsecond chanceā to catch up on discussions:
Finally, I tried to sign up for email digests but have been disappointed that Iām not getting any, presumably because I visit the forum. I still want the digests for my records, so I at least know there is one place where I can look back for stuff I know Iāve seen. Just because I drop by the site does not mean Iām reading everything thoroughly, and getting a digest gives me a second chance to catch up.