Convert Email to case related to recent opportunity

trigger CasetoAccountInsert on Case (before insert) {
     set<String> emailSet = new set<String>();
     map<String,Id> mapOpp = new map<String,Id>();
     map<String,Id> mapAcc = new map<String,Id>();
     for(Case record: Trigger.new) {
         emailSet.add(record.SuppliedEmail);
     } 
     for(Opportunity opp : [SELECT Id, AccountId, Contact_Email__c FROM Opportunity WHERE Contact_Email__c IN:emailSet ORDER BY CreatedDate DESC]){
        if(mapOpp.get(opp.Contact_Email__c) == null){
            mapOpp.put(opp.Contact_Email__c, opp.Id); 
            mapAcc.put(opp.Contact_Email__c, opp.AccountId); 
        }
    }
   for(Case cs : Trigger.new){
       cs.Related_Opportunity__c = mapOpp.get(cs.SuppliedEmail);
       cs.AccountId = mapAcc.get(cs.SuppliedEmail);
   }
}

I notice that you added Limit 1 in query.