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

TipwMX

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

property DNSPort: Integer read get_DNSPort write set_DNSPort;

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

property DNSServer: String read get_DNSServer write set_DNSServer;

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

property Idle: Boolean read get_Idle;

Default Value

true

Remarks

Idle will be False if the component is currently busy (communicating and/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

property LocalHost: String read get_LocalHost write set_LocalHost;

Default Value

''

Remarks

The LocalHost 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 multi-homed hosts (machines with more than one IP interface) setting LocalHost to the value of an interface will make the component initiate connections (or accept in the case of server components) only through that interface.

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 multi-homed 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

property MailServer: String read get_MailServer;

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

property RequestId: Integer read get_RequestId write set_RequestId;

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

property Status: String read get_Status;

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)

A timeout for the component.

Syntax

property Timeout: Integer read get_Timeout write set_Timeout;

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 raises an exception.

Please note that by default, all timeouts are inactivity timeouts, i.e. 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

function Config(ConfigurationString: String): 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)

Processes events from the internal message queue.

Syntax

procedure DoEvents();

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)

Interrupt the current method.

Syntax

procedure Interrupt();

Remarks

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

Reset Method (MX Component)

Reset the component.

Syntax

procedure Reset();

Remarks

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

Resolve Method (MX Component)

This method resolves an email address.

Syntax

procedure Resolve(EmailAddress: String);

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

type TErrorEvent = procedure (
  Sender: TObject;
  ErrorCode: Integer;
  const Description: String
) of Object;

property OnError: TErrorEvent read FOnError write FOnError;

Remarks

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

type TResponseEvent = procedure (
  Sender: TObject;
  RequestId: Integer;
  const Domain: String;
  const MailServer: String;
  Precedence: Integer;
  TimeToLive: Integer;
  StatusCode: Integer;
  const Description: String;
  Authoritative: Boolean
) of Object;

property OnResponse: TResponseEvent read FOnResponse write FOnResponse;

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)

The component accepts one or more of the following configuration settings. Configuration 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.

UDP Config Settings

Socket Config Settings

Base Config Settings

Trappable Errors (MX Component)

MX Errors

	290   No DNS server specified.
	530   Busy performing current action.

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

UDP Errors

	104   UDP is already Active.
	106   You cannot change the LocalPort while the component is Active.
	107   You cannot change the LocalHost at this time. A connection is in progress.
	109   The component must be Active for this operation.
	112   Cannot change MaxPacketSize while the component is Active.
	113   Cannot change ShareLocalPort option while the component is Active.
	114   Cannot change RemoteHost when UseConnection is set and the component Active.
	115   Cannot change RemotePort when UseConnection is set and the component is Active.
	116   RemotePort can't be zero when UseConnection is set. Please specify a valid service port number.
	117   Cannot change UseConnection while the component is Active.
	118   Message can't be longer than MaxPacketSize.
	119   Message too short.
	434   Unable to convert string to selected CodePage

SSL Errors

	270   Cannot load specified security library.
	271   Cannot open certificate store.
	272   Cannot find specified certificate.
	273   Cannot acquire security credentials.
	274   Cannot find certificate chain.
	275   Cannot verify certificate chain.
	276   Error during handshake.
	280   Error verifying certificate.
	281   Could not find client certificate.
	282   Could not find server certificate.
	283   Error encrypting data.
	284   Error decrypting data.

TCP/IP Errors

	10004   [10004] Interrupted system call.
	10009   [10009] Bad file number.
	10013   [10013] Access denied.
	10014   [10014] Bad address.
	10022   [10022] Invalid argument.
	10024   [10024] Too many open files.
	10035   [10035] Operation would block.
	10036   [10036] Operation now in progress.
	10037   [10037] Operation already in progress.
	10038   [10038] Socket operation on non-socket.
	10039   [10039] Destination address required.
	10040   [10040] Message too long.
	10041   [10041] Protocol wrong type for socket.
	10042   [10042] Bad protocol option.
	10043   [10043] Protocol not supported.
	10044   [10044] Socket type not supported.
	10045   [10045] Operation not supported on socket.
	10046   [10046] Protocol family not supported.
	10047   [10047] Address family not supported by protocol family.
	10048   [10048] Address already in use.
	10049   [10049] Can't assign requested address.
	10050   [10050] Network is down.
	10051   [10051] Network is unreachable.
	10052   [10052] Net dropped connection or reset.
	10053   [10053] Software caused connection abort.
	10054   [10054] Connection reset by peer.
	10055   [10055] No buffer space available.
	10056   [10056] Socket is already connected.
	10057   [10057] Socket is not connected.
	10058   [10058] Can't send after socket shutdown.
	10059   [10059] Too many references, can't splice.
	10060   [10060] Connection timed out.
	10061   [10061] Connection refused.
	10062   [10062] Too many levels of symbolic links.
	10063   [10063] File name too long.
	10064   [10064] Host is down.
	10065   [10065] No route to host.
	10066   [10066] Directory not empty
	10067   [10067] Too many processes.
	10068   [10068] Too many users.
	10069   [10069] Disc Quota Exceeded.
	10070   [10070] Stale NFS file handle.
	10071   [10071] Too many levels of remote in path.
	10091   [10091] Network subsystem is unavailable.
	10092   [10092] WINSOCK DLL Version out of range.
	10093   [10093] Winsock not loaded yet.
	11001   [11001] Host not found.
	11002   [11002] Non-authoritative 'Host not found' (try again or check DNS setup).
	11003   [11003] Non-recoverable errors: FORMERR, REFUSED, NOTIMP.
	11004   [11004] Valid name, no data record (check DNS setup).