The team @
GPGTools.Org released their latest version (2019.1) last week on August 22nd. New installations of this release use
keys.openpgp.org as the default key server & upgrades to this release prompt users to switch. This was known in advanced & therefore expected. However, I am noticing another issue that seems to have taken hold sometime between release 2018.5 2506n and the current version that may require some action on our part to provide continuity for users who are upgrading but opting to continue using the SKS key servers.
What I am seeing happen is when attempting to use (or switch back to) an SKS key server, the GPGTools clients will claim the server is invalid. Under the hood, I can see queries for DNS SRV records being made and returning NXDOMAIN. So one of 2 things is required to restore service: