MX Component

Properties   Methods   Events   Config Settings   Errors  

The MX component 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

nsoftware.IPWorks.MX

Remarks

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

The component operates in synchronous or asynchronous mode, depending on the value of the Timeout property. Calling the Resolve method makes the component query the DNSServer. The Response event is fired for each server that handles mail for the email address. The component 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 component with short descriptions. Click on the links for further details.

Method List

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

Event List

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

Config Settings

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

DNSPort Property (MX Component)

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

Syntax

• C#
• VB.NET

public int DNSPort { get; set; }

Public Property DNSPort As Integer

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.

DNSServer Property (MX Component)

This is the address of the DNS server.

Syntax

• C#
• VB.NET

public string DNSServer { get; set; }

Public Property DNSServer As String

Default Value

""

Remarks

This property contains the address of the DNS server. The component 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 component 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.

Idle Property (MX Component)

The current status of the component.

Syntax

• C#
• VB.NET

public bool Idle { get; }

Public ReadOnly Property Idle As Boolean

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.

LocalHost Property (MX Component)

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

Syntax

• C#
• VB.NET

public string LocalHost { get; set; }

Public Property LocalHost As String

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 component initiate connections (or accept in the case of server components) 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 component 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.

MailServer Property (MX Component)

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

Syntax

• C#
• VB.NET

public string MailServer { get; }

Public ReadOnly Property MailServer As String

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.

RequestId Property (MX Component)

This property identifies each request.

Syntax

• C#
• VB.NET

public int RequestId { get; set; }

Public Property RequestId As Integer

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 component increments RequestId automatically after sending each request.

This property is not available at design time.

Status Property (MX Component)

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#
• VB.NET

public string Status { get; }

Public ReadOnly Property Status As String

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.

Timeout Property (MX Component)

This property includes the timeout for the component.

Syntax

• C#
• VB.NET

public int Timeout { get; set; }

Public Property Timeout As Integer

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 component will wait for the operation to complete before returning control. The component will handle any potential WOULDBLOCK errors internally and automatically retry the operation for a maximum of Timeout seconds.

The component 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 component throws an exception.

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.

Config Method (MX Component)

Sets or retrieves a configuration setting.

Syntax

• C#
• VB.NET

public string Config(string configurationString);

Async Version
public async Task<string> Config(string configurationString);
public async Task<string> Config(string configurationString, CancellationToken cancellationToken);

Public Function Config(ByVal ConfigurationString As String) As String

Async Version
Public Function Config(ByVal ConfigurationString As String) As Task(Of String)
Public Function Config(ByVal ConfigurationString As String, cancellationToken As CancellationToken) As Task(Of String)

Remarks

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

These settings are similar in functionality to properties, but they are rarely used. In order to avoid "polluting" the property namespace of the component, 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.

DoEvents Method (MX Component)

This method processes events from the internal message queue.

Syntax

• C#
• VB.NET

public void DoEvents();

Async Version
public async Task DoEvents();
public async Task DoEvents(CancellationToken cancellationToken);

Public Sub DoEvents()

Async Version
Public Sub DoEvents() As Task
Public Sub DoEvents(cancellationToken As CancellationToken) As Task

Remarks

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

Interrupt Method (MX Component)

This method interrupts the current method.

Syntax

• C#
• VB.NET

public void Interrupt();

Async Version
public async Task Interrupt();
public async Task Interrupt(CancellationToken cancellationToken);

Public Sub Interrupt()

Async Version
Public Sub Interrupt() As Task
Public Sub Interrupt(cancellationToken As CancellationToken) As Task

Remarks

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

Reset Method (MX Component)

This method will reset the component.

Syntax

• C#
• VB.NET

public void Reset();

Async Version
public async Task Reset();
public async Task Reset(CancellationToken cancellationToken);

Public Sub Reset()

Async Version
Public Sub Reset() As Task
Public Sub Reset(cancellationToken As CancellationToken) As Task

Remarks

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

Resolve Method (MX Component)

This method resolves an email address.

Syntax

• C#
• VB.NET

public void Resolve(string emailAddress);

Async Version
public async Task Resolve(string emailAddress);
public async Task Resolve(string emailAddress, CancellationToken cancellationToken);

Public Sub Resolve(ByVal EmailAddress As String)

Async Version
Public Sub Resolve(ByVal EmailAddress As String) As Task
Public Sub Resolve(ByVal EmailAddress As String, cancellationToken As CancellationToken) As Task

Remarks

This method resolves an email address. Calling this method directs the component 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 Event (MX Component)

Fired when information is available about errors during data delivery.

Syntax

• C#
• VB.NET

public event OnErrorHandler OnError;

public delegate void OnErrorHandler(object sender, MXErrorEventArgs e);

public class MXErrorEventArgs : EventArgs {
  public int ErrorCode { get; }
  public string Description { get; }
}

Public Event OnError As OnErrorHandler

Public Delegate Sub OnErrorHandler(sender As Object, e As MXErrorEventArgs)

Public Class MXErrorEventArgs Inherits EventArgs
  Public ReadOnly Property ErrorCode As Integer
  Public ReadOnly Property Description As String
End Class

Remarks

The Error event is fired in case of exceptional conditions during message processing. Normally the component throws an exception.

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 Component)

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

Syntax

• C#
• VB.NET

public event OnResponseHandler OnResponse;

public delegate void OnResponseHandler(object sender, MXResponseEventArgs e);

public class MXResponseEventArgs : EventArgs {
  public int RequestId { get; }
  public string Domain { get; }
  public string MailServer { get; }
  public int Precedence { get; }
  public int TimeToLive { get; }
  public int StatusCode { get; }
  public string Description { get; }
  public bool Authoritative { get; }
}

Public Event OnResponse As OnResponseHandler

Public Delegate Sub OnResponseHandler(sender As Object, e As MXResponseEventArgs)

Public Class MXResponseEventArgs Inherits EventArgs
  Public ReadOnly Property RequestId As Integer
  Public ReadOnly Property Domain As String
  Public ReadOnly Property MailServer As String
  Public ReadOnly Property Precedence As Integer
  Public ReadOnly Property TimeToLive As Integer
  Public ReadOnly Property StatusCode As Integer
  Public ReadOnly Property Description As String
  Public ReadOnly Property Authoritative As Boolean
End Class

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 component sets the MailServer and Status properties to the best MailServer and the error or success code, respectively.

Config Settings (MX Component)

UDP Config Settings

Socket Config Settings

Base Config Settings

Trappable Errors (MX Component)

MX Errors

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

UDP Errors

SSL Errors

TCP/IP Errors