I upgraded Mac OS on the server and it erased Ensignia and restored SquirrelMail

If you had Ensignia installed inside your default SquirrelMail directory it was most likely replaced by the update. You'll need to replace your SquirrelMail with Ensignia again following the upgrade step-by-step guide.

To avoid this in the future you will need to either install Ensignia in a different directory or use the command "chattr ‐R +i" on the Ensignia folder to keep it from being updated.