MX Class

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The MX class enables querying of mail exchange (MX) records from a Domain Name Server (DNS). Thus, it will find out the names of the mail servers accepting email for a given email address or domain.

Syntax

MX

Remarks

The class will attempt to automatically determine the name of a DNS server from the system settings or from the value of the DNSServer property.

The class operates in synchronous or asynchronous mode, depending on the value of the Timeout property. Calling the Resolve method makes the class query the DNSServer. The Response event is fired for each server that handles mail for the email address. The class will fill out the MailServer property with the most preferred mail server and will set the Status property to "OK" or to an error message upon completion.

The RequestId property may be used to identify requests and is used in the Response event. The user may set its value before sending out requests and then match the responses to the request using the RequestId parameter in the Response event.

Property List

The following is the full list of the properties of the class with short descriptions. Click on the links for further details.

Method List

The following is the full list of the methods of the class with short descriptions. Click on the links for further details.

Event List

The following is the full list of the events fired by the class with short descriptions. Click on the links for further details.

Config Settings

The following is a list of config settings for the class with short descriptions. Click on the links for further details.

DNSPort Property (MX Class)

This property includes the port where the DNS server is listening.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
int GetDNSPort();
int SetDNSPort(int iDNSPort);

Unicode (Windows)
INT GetDNSPort();
INT SetDNSPort(INT iDNSPort);

int ipworks_mx_getdnsport(void* lpObj);
int ipworks_mx_setdnsport(void* lpObj, int iDNSPort);

int GetDNSPort();
int SetDNSPort(int iDNSPort);

Default Value

53

Remarks

This property contains the port where the DNS server is listening. The default value is 53, but you may set this property to any other value for use with experimental servers and such.

This property is not available at design time.

Data Type

Integer

DNSServer Property (MX Class)

This is the address of the DNS server.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
char* GetDNSServer();
int SetDNSServer(const char* lpszDNSServer);

Unicode (Windows)
LPWSTR GetDNSServer();
INT SetDNSServer(LPCWSTR lpszDNSServer);

char* ipworks_mx_getdnsserver(void* lpObj);
int ipworks_mx_setdnsserver(void* lpObj, const char* lpszDNSServer);

QString GetDNSServer();
int SetDNSServer(QString qsDNSServer);

Default Value

""

Remarks

This property contains the address of the DNS server. The class attempts to find the default DNS server for the machine where it is installed, and provide it in the DNSServer property. You may change it to any particular DNS server you want to query. While any internet host running a DNS service will suffice, it is preferable to use either the DNS server for your network or the DNS server for the domain that you are querying.

If the class cannot determine the default DNS server address, the property value will be an empty string.

Note: Automatic discovery of the default DNS server is not supported in the Java edition.

This property is not available at design time.

Data Type

String

Idle Property (MX Class)

The current status of the class.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
int GetIdle();

Unicode (Windows)
BOOL GetIdle();

int ipworks_mx_getidle(void* lpObj);

bool GetIdle();

Default Value

TRUE

Remarks

This property will be False if the component is currently busy (communicating or waiting for an answer), and True at all other times.

This property is read-only.

Data Type

Boolean

LocalHost Property (MX Class)

The name of the local host or user-assigned IP interface through which connections are initiated or accepted.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
char* GetLocalHost();
int SetLocalHost(const char* lpszLocalHost);

Unicode (Windows)
LPWSTR GetLocalHost();
INT SetLocalHost(LPCWSTR lpszLocalHost);

char* ipworks_mx_getlocalhost(void* lpObj);
int ipworks_mx_setlocalhost(void* lpObj, const char* lpszLocalHost);

QString GetLocalHost();
int SetLocalHost(QString qsLocalHost);

Default Value

""

Remarks

This property contains the name of the local host as obtained by the gethostname() system call, or if the user has assigned an IP address, the value of that address.

In multihomed hosts (machines with more than one IP interface) setting LocalHost to the IP address of an interface will make the class initiate connections (or accept in the case of server classs) only through that interface. It is recommended to provide an IP address rather than a hostname when setting this property to ensure the desired interface is used.

If the class is connected, the LocalHost property shows the IP address of the interface through which the connection is made in internet dotted format (aaa.bbb.ccc.ddd). In most cases, this is the address of the local host, except for multihomed hosts (machines with more than one IP interface).

Note: LocalHost is not persistent. You must always set it in code, and never in the property window.

Data Type

String

MailServer Property (MX Class)

This property includes the mail server with the lowest precedence value (lowest cost to reach).

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
char* GetMailServer();

Unicode (Windows)
LPWSTR GetMailServer();

char* ipworks_mx_getmailserver(void* lpObj);

QString GetMailServer();

Default Value

""

Remarks

This property contains the mail server with lowest precedence value (lowest cost to reach). After all events are fired, this property holds the name of the best mail server for the supplied email address, and the Status property holds the completion status.

This property is read-only.

Data Type

String

RequestId Property (MX Class)

This property identifies each request.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
int GetRequestId();
int SetRequestId(int iRequestId);

Unicode (Windows)
INT GetRequestId();
INT SetRequestId(INT iRequestId);

int ipworks_mx_getrequestid(void* lpObj);
int ipworks_mx_setrequestid(void* lpObj, int iRequestId);

int GetRequestId();
int SetRequestId(int iRequestId);

Default Value

0

Remarks

This property identifies each request. This may be useful if several email addresses need to be resolved. Each request may be identified by the user before starting a query by calling the Resolve method.

If a custom value is needed for RequestId, the property must be set before resolving an email address. The class increments RequestId automatically after sending each request.

This property is not available at design time.

Data Type

Integer

Status Property (MX Class)

The status of the request is empty while in progress. This property is set to OK or to an error message upon completion.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
char* GetStatus();

Unicode (Windows)
LPWSTR GetStatus();

char* ipworks_mx_getstatus(void* lpObj);

QString GetStatus();

Default Value

""

Remarks

This property is reset each time the Resolve method is called. When a response comes from the DNSServer, this property is set to "OK" in case of success or to an error message as described in the Response event.

This property is read-only.

Data Type

String

Timeout Property (MX Class)

This property includes the timeout for the class.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
int GetTimeout();
int SetTimeout(int iTimeout);

Unicode (Windows)
INT GetTimeout();
INT SetTimeout(INT iTimeout);

int ipworks_mx_gettimeout(void* lpObj);
int ipworks_mx_settimeout(void* lpObj, int iTimeout);

int GetTimeout();
int SetTimeout(int iTimeout);

Default Value

60

Remarks

If the Timeout property is set to 0, all operations return immediately, potentially failing with a WOULDBLOCK error if data cannot be sent immediately.

If Timeout is set to a positive value, data is sent in a blocking manner and the class will wait for the operation to complete before returning control. The class will handle any potential WOULDBLOCK errors internally and automatically retry the operation for a maximum of Timeout seconds.

The class will use DoEvents to enter an efficient wait loop during any potential waiting period, making sure that all system events are processed immediately as they arrive. This ensures that the host application does not freeze and remains responsive.

If Timeout expires, and the operation is not yet complete, the class fails with an error.

Note: By default, all timeouts are inactivity timeouts, that is, the timeout period is extended by Timeout seconds when any amount of data is successfully sent or received.

The default value for the Timeout property is 60 seconds.

Data Type

Integer

Config Method (MX Class)

Sets or retrieves a configuration setting.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
char* Config(const char* lpszConfigurationString);

Unicode (Windows)
LPWSTR Config(LPCWSTR lpszConfigurationString);

char* ipworks_mx_config(void* lpObj, const char* lpszConfigurationString);

QString Config(const QString& qsConfigurationString);

Remarks

Config is a generic method available in every class. It is used to set and retrieve configuration settings for the class.

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the class, access to these internal properties is provided through the Config method.

To set a configuration setting named PROPERTY, you must call Config("PROPERTY=VALUE"), where VALUE is the value of the setting expressed as a string. For boolean values, use the strings "True", "False", "0", "1", "Yes", or "No" (case does not matter).

To read (query) the value of a configuration setting, you must call Config("PROPERTY"). The value will be returned as a string.

Error Handling (C++)

This method returns a String value; after it returns, call the GetLastErrorCode() method to obtain its result code; 0 indicates success, while a non-zero error code indicates that this method encountered an error during its execution. If an error occurs, the GetLastError() method can be called to retrieve the associated error message.

DoEvents Method (MX Class)

This method processes events from the internal message queue.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
int DoEvents();

Unicode (Windows)
INT DoEvents();

int ipworks_mx_doevents(void* lpObj);

int DoEvents();

Remarks

When DoEvents is called, the class processes any available events. If no events are available, it waits for a preset period of time, and then returns.

Error Handling (C++)

This method returns a result code; 0 indicates success, while a non-zero error code indicates that this method encountered an error during its execution. If an error occurs, the GetLastError() method can be called to retrieve the associated error message. (Note: This method's result code can also be obtained by calling the GetLastErrorCode() method after it returns.)

Interrupt Method (MX Class)

This method interrupts the current method.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
int Interrupt();

Unicode (Windows)
INT Interrupt();

int ipworks_mx_interrupt(void* lpObj);

int Interrupt();

Remarks

If there is no method in progress, Interrupt simply returns, doing nothing.

Error Handling (C++)

This method returns a result code; 0 indicates success, while a non-zero error code indicates that this method encountered an error during its execution. If an error occurs, the GetLastError() method can be called to retrieve the associated error message. (Note: This method's result code can also be obtained by calling the GetLastErrorCode() method after it returns.)

Reset Method (MX Class)

This method will reset the class.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
int Reset();

Unicode (Windows)
INT Reset();

int ipworks_mx_reset(void* lpObj);

int Reset();

Remarks

This method will reset the class's properties to their default values.

Error Handling (C++)

This method returns a result code; 0 indicates success, while a non-zero error code indicates that this method encountered an error during its execution. If an error occurs, the GetLastError() method can be called to retrieve the associated error message. (Note: This method's result code can also be obtained by calling the GetLastErrorCode() method after it returns.)

Resolve Method (MX Class)

This method resolves an email address.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
int Resolve(const char* lpszEmailAddress);

Unicode (Windows)
INT Resolve(LPCWSTR lpszEmailAddress);

int ipworks_mx_resolve(void* lpObj, const char* lpszEmailAddress);

int Resolve(const QString& qsEmailAddress);

Remarks

This method resolves an email address. Calling this method directs the class to query DNSServer at port DNSPort about MX records related to EmailAddress.

The server's response is provided through one or more Response events.

After the query completes, the MailServer property is set to the best mail server and the Status property includes the result description of the response.

Valid queries are email addresses like name@company.com or hostnames and domains like domain.com.

Example. Determine Top Priority Mail Server of Email Address:

MXControl.Resolve "email@server.com" While MXControl.MailServer = "" MXControl.DoEvents() End While BestMailServer = MXControl.MailServer

Error Handling (C++)

This method returns a result code; 0 indicates success, while a non-zero error code indicates that this method encountered an error during its execution. If an error occurs, the GetLastError() method can be called to retrieve the associated error message. (Note: This method's result code can also be obtained by calling the GetLastErrorCode() method after it returns.)

Error Event (MX Class)

Fired when information is available about errors during data delivery.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
virtual int FireError(MXErrorEventParams *e);

typedef struct {
  int ErrorCode;
  const char *Description;
  int reserved;
} MXErrorEventParams;


Unicode (Windows)
virtual INT FireError(MXErrorEventParams *e);

typedef struct {
  INT ErrorCode;
  LPCWSTR Description;
  INT reserved;
} MXErrorEventParams;

#define EID_MX_ERROR 1

virtual INT IPWORKS_CALL FireError(INT &iErrorCode, LPSTR &lpszDescription);

class MXErrorEventParams {
public:
  int ErrorCode();

  const QString &Description();

  int EventRetVal();
  void SetEventRetVal(int iRetVal);
};

// To handle, connect one or more slots to this signal.
void Error(MXErrorEventParams *e);

// Or, subclass MX and override this emitter function.
virtual int FireError(MXErrorEventParams *e) {...}

Remarks

The Error event is fired in case of exceptional conditions during message processing. Normally the class fails with an error.

The ErrorCode parameter contains an error code, and the Description parameter contains a textual description of the error. For a list of valid error codes and their descriptions, please refer to the Error Codes section.

Response Event (MX Class)

This event is fired for each MailServer accepting email for the domain.

Syntax

• C++
• C
• Qt

ANSI (Cross Platform)
virtual int FireResponse(MXResponseEventParams *e);

typedef struct {
  int RequestId;
  const char *Domain;
  const char *MailServer;
  int Precedence;
  int TimeToLive;
  int StatusCode;
  const char *Description;
  int Authoritative;
  int reserved;
} MXResponseEventParams;


Unicode (Windows)
virtual INT FireResponse(MXResponseEventParams *e);

typedef struct {
  INT RequestId;
  LPCWSTR Domain;
  LPCWSTR MailServer;
  INT Precedence;
  INT TimeToLive;
  INT StatusCode;
  LPCWSTR Description;
  BOOL Authoritative;
  INT reserved;
} MXResponseEventParams;

#define EID_MX_RESPONSE 2

virtual INT IPWORKS_CALL FireResponse(INT &iRequestId, LPSTR &lpszDomain, LPSTR &lpszMailServer, INT &iPrecedence, INT &iTimeToLive, INT &iStatusCode, LPSTR &lpszDescription, BOOL &bAuthoritative);

class MXResponseEventParams {
public:
  int RequestId();

  const QString &Domain();

  const QString &MailServer();

  int Precedence();

  int TimeToLive();

  int StatusCode();

  const QString &Description();

  bool Authoritative();

  int EventRetVal();
  void SetEventRetVal(int iRetVal);
};

// To handle, connect one or more slots to this signal.
void Response(MXResponseEventParams *e);

// Or, subclass MX and override this emitter function.
virtual int FireResponse(MXResponseEventParams *e) {...}

Remarks

A Response event is fired for each mail server handling email for the requested domain. The RequestId parameter identifies the request and equals the value of RequestId property right before the Resolve method is called. MailServer is the name of the server handling the email for the requested Domain. A lower Precedence value should be preferred. The TimeToLive parameter gives the validity time in seconds before the DNSServer should be queried again.

Possible values for the StatusCode and Description parameters are as follows:

After the last Response event is fired, the class sets the MailServer and Status properties to the best MailServer and the error or success code, respectively.

Config Settings (MX Class)

UDP Config Settings

Socket Config Settings

Base Config Settings

Trappable Errors (MX Class)

Error Handling (C++)

Call the GetLastErrorCode() method to obtain the last called method's result code; 0 indicates success, while a non-zero error code indicates that this method encountered an error during its execution. Known error codes are listed below. If an error occurs, the GetLastError() method can be called to retrieve the associated error message.

MX Errors

The class may also return one of the following error codes, which are inherited from other classes.

UDP Errors

SSL Errors

TCP/IP Errors