Whe the onionmail server starts the first time, it negotiates some F(X) function to another servers:
Then delete via wipe the encrypted keyblock.txt and change the master key.
All F(X) have some block, counter limitations.
When the server starts ti try to run the function F(X) to get the master key.

If the syop of the server sends the autodestruction certificate KCTL, all function F(X) are destroyed and the onionmail server become unusable: