有各 xxxx.pas的源文件，要把它封装到dll中去使用，dll如何定义，在项目中如何调用？

有如下xxxx.pas部分:Unit xxxx;interface
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;type
  TMapiErrEvent = procedure(Sender: TObject; ErrCode: Integer) of object;  TMapiControl = class(TComponent)
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;
  private
    { Private-Deklarationen }
    FSubject: string;
    FMailtext: string;
    FFromName: string;
    FFromAdress: string;
    FTOAdr: TStrings;
    FCCAdr: TStrings;
    FBCCAdr: TStrings;
    FAttachedFileName: TStrings;
    FDisplayFileName: TStrings;
    FShowDialog: Boolean;
    FUseAppHandle: Boolean;
    { Error Events: }
    FOnUserAbort: TNotifyEvent;
    FOnMapiError: TMapiErrEvent;
    FOnSuccess: TNotifyEvent;    procedure SetToAddr(newValue: TStrings);
    procedure SetCCAddr(newValue: TStrings);
    procedure SetBCCAddr(newValue: TStrings);
    procedure SetAttachedFileName(newValue: TStrings);
  protected
    { Protected-Deklarationen }
  public
    { Public-Deklarationen }
    ApplicationHandle: THandle;
    procedure Sendmail();
    procedure Reset();
  published
    { Published-Deklarationen }
    property Subject: string read FSubject write FSubject;
    property Body: string read FMailText write FMailText;
    property FromName: string read FFromName write FFromName;
    property FromAdress: string read FFromAdress write FFromAdress;
    property Recipients: TStrings read FTOAdr write SetTOAddr;
    property CopyTo: TStrings read FCCAdr write SetCCAddr;
    property BlindCopyTo: TStrings read FBCCAdr write SetBCCAddr;
    property AttachedFiles: TStrings read FAttachedFileName write SetAttachedFileName;
    property DisplayFileName: TStrings read FDisplayFileName;
    property ShowDialog: Boolean read FShowDialog write FShowDialog;
    property UseAppHandle: Boolean read FUseAppHandle write FUseAppHandle;    { Events: }
    property OnUserAbort: TNotifyEvent read FOnUserAbort write FOnUserAbort;
    property OnMapiError: TMapiErrEvent read FOnMapiError write FOnMapiError;
    property OnSuccess: TNotifyEvent read FOnSuccess write FOnSuccess;
  end;procedure Register;implementationuses Mapi;{ Register the component: }procedure Register;
begin
  RegisterComponents('expectIT', [TMapiControl]);
end;{ TMapiControl }constructor TMapiControl.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  FOnUserAbort := nil;
  FOnMapiError := nil;
  FOnSuccess := nil;
  .........
怎样封装到DLL中，如何使用dll？？？？？