Fix AltPlugin.mailbundle after MacOS updates

altermail.sh

#!/bin/sh

# Check if running as root
if [ "$(id -u)" != "0" ]; then
   echo "This script must be run as root" 1>&2
   exit 1
fi

token=`cat /System/Applications/Mail.app/Contents/Info.plist | grep -A1 "PluginCompatibilityUUID" | grep string | sed 's/<string>//' | sed 's/<\/string>//'`
path="/Library/Mail/Bundles/AltPlugin.mailbundle/Contents/Info.plist"
osver=`sw_vers -productVersion`

# make sure it doesn't contain the $token
if [ `/usr/libexec/Plistbuddy -c "Print Supported${osver}PluginCompatibilityUUIDs" $path | grep -c $token` -ne 0 ]; then
  # add the token to the array
  echo "Token already exists, quitting..."
  exit 1
fi

# Killing Mail.app
killall -9 Mail

# Add the token to the key values of "Supportedd${osver}PluginCompatibilityUUIDs"
echo "Adding token: $token"
/usr/libexec/PlistBuddy -c "Add :Supported${osver}PluginCompatibilityUUIDs: string $token" $path

if (( $? == 0 )); then
  echo "Successfully added token to Info.plist"
else
  echo "Failed to add token to Info.plist, quitting..."
  exit 1
fi


echo "Running codesign"
codesign -f -s - /Library/Mail/Bundles/AltPlugin.mailbundle
if (( $? == 0 )); then
  echo "codesign done!"
else
  echo "codesign failed!"
fi


echo "Running spctl"
sudo spctl --add --label "Allow AltPlugin to load" /Library/Mail/Bundles/AltPlugin.mailbundle
if (( $? == 0 )); then
  echo "spctl done!"
  exit 0
else
  echo "spctl failed!"
  exit 1
fi

Thanks!
Works like a charm