trigger RunLeadAutoResponseRules on Lead (after insert) {

    List<LeadnewlyInsertedLeads = [SELECT Id From Lead WHERE Id IN :trigger.new]; 
    Database.DMLOptions dmo = new Database.DMLOptions();
	
    dmo.emailHeader.triggerUserEmail = true;
	
    for (Lead l : newlyInsertedLeads ) { 
        Database.update(l, dmo); 
    }     
    
}

It’s a good idea to limit this type of trigger to only run for certain types of leads, so a suggestion is to add a check for specific Lead Source, such as LeadSource == 'Web'… Read more