This feature exists in Mozilla Thunderbird, which I have used in the past. Essentially, it is the ability to connect to an online GAL (Global Address List) which contains emails of every individual in the organization that I am a part of. These are stored on a server and accessed through a URL by the mail client. This is a guide I found on said feature for Thunderbird if it is of any help in describing it: How To Access Global Address List From Thunderbird Mail Client - Intermedia Knowledge Base
I use Mailspring with my university email, and it is helpful to be able to simply type in someone’s name to get their email address immediately in my mail client, rather than having to go look at the online directory myself to find the correct one.
(Originally posted by salikhov on GitHub.)
(Original post had 12 upvotes.)