InvalidateEmails.findEmailFields.cls

 private static Map < String, List < String >> findEmaiLFields() {
  Map < String, List < String >> soEmailFieldMap = new Map < String, List < String >> ();
  // Iterate over all SObjects
  for (SObjectType soType: Schema.getGlobalDescribe().values()) {
   DescribeSObjectResult soDescribe = soType.getDescribe();
   // Skip objects we cannot query or update
   if (!soDescribe.isQueryable() || !soDescribe.isUpdateable()) continue;
   String objectTypeName = soDescribe.getName();
   // Iterate over all fields found on a given SObject
   for (SObjectField soField: soDescribe.fields.getMap().values()) {
    DescribeFieldResult field = soField.getDescribe();
    // Skip non Email type fields
    if (field.getType() != Schema.DisplayType.EMAIL) continue;
    // Skip emails that cannot be filtered on
    if (!field.isFilterable()) continue;
    // Collect all Email fields found
    if (soEmailFieldMap.containsKey(objectTypeName)) {
     soEmailFieldMap.get(objectTypeName).add(field.getName());
    } else {
     soEmailFieldMap.put(objectTypeName, new List < String > {
      field.getName()
     });
    }
   }
  }
  return soEmailFieldMap;
 }