NonMatchedAccountExporter.cls

class NonMatchedAccountExporter {

	public void run(List_MRK__c listID) {
		Boolean moreToProcess = execute(listID);
		while(moreToProcess = true) {
			moreToProcess = execute(listID);
		}
	}

	public Boolean execute(List_MRK__c listID) {
		// SOQL to return non-matchs List Attachment Item records up 2000
		// [select Item_ID_MRK__c from List_Attachment_Item where limit 2000]
		String idsString = '';

		for (List_Attachment_Item lai : [select Item_ID_MRK__c from List_Attachment_Item where limit 2000]) {
			idsString = idsString + lai.Item_ID_MRK__c + '\n';	
		}

		

		// Assume these methods will already exist
		//AttachmentServices.createAttachment(listID, idsString)
		//AttachmentServices.appendToAttachment(listID, idsString)

		return records.size() == 2000;
	}

}