This is the example.com OpenPGP Web Key Directory (WKD) service. WKD allows an outside user, using an appropriate email client, to discover and import, through authoritative channels, a future corresponds OpenPGP public key, without using third party servers. This server provides the advanced method of key discovery as described in the network working group specification §3.1 - Key Discovery.
If you have an email address on the example.com domain, you may publish your public key via the WKD Update Protocol, or by sending an unencrypted message to the submission-address; wkd-submission@example.com with your public key as an attachment.
If you have already submitted your key, you may confirm its availability via the WKD Checker site.
Please note, it may take up to 30 minutes, after your key has been confirmed, before it is available to the public.
For more information on how to use this service, see the GnuPG wiki article Web Key Directory (WKD).
For information on building a service similar to this, see the GnuPG wiki article Web Key Service (WKS),
or the OpenPGP WKD Network Working Group specification.