             self.addHeaders(keyValuePairs)
         }
         
-        public func addAttachment(filename: String, data: NSData, cid: String?) {
+        public func addAttachment(filename: String, data: NSData, cid: String? = nil) {
             if self.attachments == nil {
                 self.attachments = [filename: data]
             } else {

            }
        }
        
        public func setTos(addresses: [String], names: [String]?) throws {
            if self.hasRecipientsInSmtpApi {
                try self.smtpapi.setTos(addresses, names: names)
            } else {

        // MARK: FUNCTIONS
        //=========================================================================
        
        public func addTo(address: String, name: String? = nil) throws {
            var names: [String]?
            if let n = name {
                names = [n]
