SMTP安全认证的邮件附件发送不正确问题(100分)

//一个演示程序，
//窗体上有一个BUTTON控件，一个LABEL控件，一个NMSMTP控件
//带密码险证的邮件发送程序需要BASE64编码，DecodeBase64和 EncodeBase64
//为解码和编码函数

unit Unit1;

interface

uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
StdCtrls, Psock, NMsmtp, ComCtrls;

type
TForm1 = class(TForm)
NMSMTP1: TNMSMTP;
Button1: TButton;
Label1: TLabel;
procedure Button1Click(Sender: TObject);
procedure NMSMTP1Connect(Sender: TObject);
procedure NMSMTP1InvalidHost(var Handled: Boolean);
procedure NMSMTP1ConnectionFailed(Sender: TObject);
procedure NMSMTP1Status(Sender: TComponent; Status: String);
procedure NMSMTP1SendStart(Sender: TObject);
procedure NMSMTP1Success(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
//BaseTable为BASE64码表
const BaseTable:string='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';

var
Form1: TForm1;
AuthSucc:boolean;// 是否需要密码验证
function DecodeBase64(Source:string):string; //解码函数
function FindInTable(CSource:char):integer; //
function EncodeBase64(Source:string):string; //编码函数
implementation

{$R *.DFM}
//
function FindInTable(CSource:char):integer;
begin
result:=Pos(string(CSource),BaseTable)-1;
end;
////
function DecodeBase64(Source:string):string;
var
SrcLen,Times,i:integer;
x1,x2,x3,x4,xt:byte;
begin
result:='';
SrcLen:=Length(Source);
Times:=SrcLen div 4;
for i:=0 to Times-1 do
begin
x1:=FindInTable(Source[1+i*4]);
x2:=FindInTable(Source[2+i*4]);
x3:=FindInTable(Source[3+i*4]);
x4:=FindInTable(Source[4+i*4]);
x1:=x1 shl 2;
xt:=x2 shr 4;
x1:=x1 or xt;
x2:=x2 shl 4;
result:=result+chr(x1);
if x3= 64 then break;
xt:=x3 shr 2;
x2:=x2 or xt;
x3:=x3 shl 6;
result:=result+chr(x2);
if x4=64 then break;
x3:=x3 or x4;
result:=result+chr(x3);
end;
end;
/////
function EncodeBase64(Source:string):string;
var
Times,LenSrc,i:integer;
x1,x2,x3,x4:char;
xt:byte;
begin
result:='';
LenSrc:=length(Source);
if LenSrc mod 3 =0 then Times:=LenSrc div 3
else Times:=LenSrc div 3 + 1;
for i:=0 to times-1 do
begin
if LenSrc >= (3+i*3) then
begin
x1:=BaseTable[(ord(Source[1+i*3]) shr 2)+1];
xt:=(ord(Source[1+i*3]) shl 4) and 48;
xt:=xt or (ord(Source[2+i*3]) shr 4);
x2:=BaseTable[xt+1];
xt:=(Ord(Source[2+i*3]) shl 2) and 60;
xt:=xt or (ord(Source[3+i*3]) shr 6);
x3:=BaseTable[xt+1];
xt:=(ord(Source[3+i*3]) and 63);
x4:=BaseTable[xt+1];
end
else if LenSrc>=(2+i*3) then
begin
x1:=BaseTable[(ord(Source[1+i*3]) shr 2)+1];
xt:=(ord(Source[1+i*3]) shl 4) and 48;
xt:=xt or (ord(Source[2+i*3]) shr 4);
x2:=BaseTable[xt+1];
xt:=(ord(Source[2+i*3]) shl 2) and 60;
x3:=BaseTable[xt+1];
x4:='=';
end else
begin
x1:=BaseTable[(ord(Source[1+i*3]) shr 2)+1];
xt:=(ord(Source[1+i*3]) shl 4) and 48;
x2:=BaseTable[xt+1];
x3:='=';
x4:='=';
end;
result:=result+x1+x2+x3+x4;
end;
end;
//////////
procedure TForm1.Button1Click(Sender: TObject);
var MailTo,MailBody:TStringList;
begin
Nmsmtp1.Host :='smtp.sohu.com';
nmsmtp1.Port :=25;
nmsmtp1.UserID :='linbch';//发信人的用户名，必须是真实的
nmsmtp1.ReportLevel :=1;
Nmsmtp1.TimeOut :=10000;
nmsmtp1.Connect ; ///连接
if AuthSucc=true then ////验证成功
begin
MailTo:=TStringList.Create;
MailTo.Add('cunmin1@163.net');
MailBody.Add('Hello it is a test');
nmsmtp1.PostMessage.FromAddress:='linbch@sohu.com'; //发信人的电子邮件地址
nmsmtp1.PostMessage.ToAddress :=MailTo;
nmsmtp1.PostMessage.Body:=MailBody;
nmsmtp1.PostMessage.Subject :='My test';
Mailto.Clear ;
Mailto.Add('c:/a.mdb');
Mailto.Add('c:/b.txt');
nmsmtp1.PostMessage.Attachments:=MailTo; 附件
MailTo.Free ;
MailBody.Free;
nmsmtp1.SendMail;
end;
end;
procedure TForm1.NMSMTP1Connect(Sender: TObject);
begin
//////连接成功，下面用户认证过程
label1.caption:=nmsmtp1.Status;
if nmsmtp1.ReplyNumber = 250 then
label1.caption:=nmsmtp1.Transaction('auth login'); //开始认证
if nmsmtp1.ReplyNumber =334 then //返回值为334，让你输入用BASE64编码后的用户名
label1.caption:=nmsmtp1.Transaction('YWFhYWE=');// 用户名aaaaa
if nmsmtp1.ReplyNumber =334 then // 返回值为334，让你输入用BASE64编码后的用户密码
label1.caption:=nmsmtp1.Transaction('MTIzNDU2'); //密码为123456
if nmsmtp1.ReplyNumber =235 then
begin
label1.caption:='successful';
AuthSucc:=true;
end;
//showmessage(label1.caption);
end;

procedure TForm1.NMSMTP1InvalidHost(var Handled: Boolean);
begin
label1.caption :='Invalid Host';
end;

procedure TForm1.NMSMTP1ConnectionFailed(Sender: TObject);
begin
label1.caption :='connect failed';
end;

procedure TForm1.NMSMTP1Status(Sender: TComponent; Status: String);
begin
label1.caption :=nmsmtp1.Status ;
end;

procedure TForm1.NMSMTP1SendStart(Sender: TObject);
begin
label1.Caption :='start send';
end;

procedure TForm1.NMSMTP1Success(Sender: TObject);
begin
label1.Caption:='send success!';
end;

end.

===========================================================
我用上面的程序发送附件时，小文件b.txt发送成功，但大文件a.mdb（140K），收到后 Access竟然打不开，文件长度变为12K，这是什么原因？怎样改？

Internet邮件协议只能发送ASCII32-254的字符集。必须把二进制文件转换成TXT文件。

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