Timeline
Maintenance began. The relay directory was frozen, and mailbox relays continued to accept messages but held them.
The nine directory signers moved to new keys that support the hybrid signatures used by Glossia 4.0.
Every relay confirmed it could read the new directory.
Maintenance ended. Held messages were released and delivered within six minutes.
What happened
The window was announced in clients and on this site three weeks in advance, and timed for the hours when the fewest people use Glossia worldwide. Messages sent during the window were accepted, held and delivered when it ended.