pop3接收邮件出现乱码问题

如题我用delphi练习写了一个简答的邮件接收程序，但是邮件主题和接收到的邮件内容，有部分可以正常显示，有部分却是乱码。我已经在网上找了一个解码函数base64函数。但是还是有部分不能正常读出邮件主题和邮件内容。好像发邮件可会有这个问题，所以发邮件的代码暂时没写
我把代码贴出：
unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, Menus, ImgList, IdMessage, IdBaseComponent, IdComponent,
  IdTCPConnection, IdTCPClient, IdMessageClient, IdSMTP, ExtCtrls, sPanel,
  StdCtrls, sMemo, ComCtrls, sListView, sStatusBar, sSkinManager, ToolWin,
  sToolBar, IdPOP3, sDialogs, IdAntiFreezeBase, IdAntiFreeze, IdCoder,
  IdCoder3to4, IdCoderMIME;type
  TFormMain = class(TForm)
    sPanel1: TsPanel;
    IdSMTP1: TIdSMTP;
    IdMessage1: TIdMessage;
    MainMenu1: TMainMenu;
    ImageList1: TImageList;
    N1: TMenuItem;
    N2: TMenuItem;
    N3: TMenuItem;
    N4: TMenuItem;
    N5: TMenuItem;
    sToolBar1: TsToolBar;
    sSkinManager1: TsSkinManager;
    ToolButton1: TToolButton;
    sStatusBar1: TsStatusBar;
    lvMail: TsListView;
    memoMail: TsMemo;
    lvAttach: TsListView;
    IdPOP31: TIdPOP3;
    ToolButton3: TToolButton;
    sSaveDialog1: TsSaveDialog;
    sOpenDialog1: TsOpenDialog;
    IdAntiFreeze1: TIdAntiFreeze;
    N6: TMenuItem;
    IdDecoderMIME1: TIdDecoderMIME;
    IdEncoderMIME1: TIdEncoderMIME;
    procedure N2Click(Sender: TObject);
    procedure lvAttachDblClick(Sender: TObject);
    procedure lvMailDblClick(Sender: TObject);
    procedure N6Click(Sender: TObject);
    function DecodeBase64(s: string): String;
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  FormMain: TFormMain;implementation
uses unit2;
{$R *.dfm}
//----Base64编码转换----//
function TFormMain.DecodeBase64(s: string): String;
var
  s1,s2,s3: integer;
  t,v: string;
  Encoding: char;
  hex,step: integer;
  a1: array[1..4] of byte;
  b1: array[1..3] of byte;
  j:  integer;
  byte_ptr,real_bytes: integer;
begin
  s1:=Pos('=?',s);
  s2:= 1 ;
  hex:= 0 ;
  if s1>0 then
  begin
    for s2:=Length(s)-1 downto 1 do
    begin
      if Copy(s,s2,2)='?=' then Break;
    end;
  end;
  if (s1=0) or (s2=1) then
  begin
    Result:=s;
    Exit;
  end;
  t:=Copy(s,s1+2,s2-2-s1);
  s3:=Pos('?',t);
  Delete(t,1,s3);
  if(t='')then
  begin
    Result:= s;
    Exit ;
  end ;
  Encoding:=t[1];
  Delete(t,1,2);
  v:='';
  step:=0;
  case Encoding of
  'Q':
    while t<>'' do
    begin
      case step of
      0:
        begin
          case t[1] of
          '_': v:=v+' ';
          '=': step:=1;
          else v:=v+t[1];
          end;
        end;
      1:
        begin
          if t[1]<='9' then hex:=(Ord(t[1])-Ord('0'))*16
          else hex:=(Ord(t[1])-55)*16;
          step:=2;
        end;
      2:
        begin
          if t[1]<='9' then hex:=hex+(Ord(t[1])-Ord('0'))
          else hex:=hex+Ord(t[1])-55;
          v:=v+Chr(hex);
          step:=0;
        end;
      end;
      Delete(t,1,1);
    end;
  'B':
    begin
      byte_ptr:=0;
      for j:=1 to Length(t) do
      begin
              Inc(byte_ptr);
              case t[j] of
              'A'..'Z': a1[byte_ptr]:=Ord(t[j])-65;
              'a'..'z': a1[byte_ptr]:=Ord(t[j])-71;
              '0'..'9': a1[byte_ptr]:=Ord(t[j])+4;
              '+': a1[byte_ptr]:=62;
              '/': a1[byte_ptr]:=63;
              '=': a1[byte_ptr]:=64;
              end;
              if byte_ptr=4 then
              begin
                      byte_ptr:=0;
                      real_bytes:=3;
                      if a1[1]=64 then real_bytes:=0;
                      if a1[3]=64 then
                      begin
                              a1[3]:=0;
                              a1[4]:=0;
                              real_bytes:=1;
                      end;
                      if a1[4]=64 then
                      begin
                              a1[4]:=0;
                              real_bytes:=2;
                      end;
                      b1[1]:=a1[1]*4+(a1[2] div 16);
                      b1[2]:=(a1[2] mod 16)*16+(a1[3]div 4);
                      b1[3]:=(a1[3] mod 4)*64 +a1[4];
                      if(real_bytes>0)then
                        v:= v + chr(b1[1]) ;
                      if(real_bytes>1)then
                        v:= v + chr(b1[2]) ;
                      if(real_bytes>2)then
                        v:= v + chr(b1[3]) ;
              end;
      end;
    end;
  end;
  Result := v;
end;procedure TFormMain.N2Click(Sender: TObject);
var
Index:Integer;
MailSum:dword;
MailItem:TlistItem;
begin  lvmail.Items.Clear;
  if IdPOP31.Connected then
  begin
  IdPOP31.Connect;
  end
  else
  begin
    IdPOP31.Host:=FormConfig.edtPOP3.Text;
    IdPOP31.Port:=strtoint(formconfig.edtPOP3port.text);
    IdPOP31.Username:=FormConfig.edtUser.Text;
    IdPOP31.Password:=FormConfig.edtPW.text;
    IdPOP31.Connect;
    Mailsum:=Idpop31.CheckMessages;//获得邮件数
    if MailSum > 0 then
      sStatusBar1.SimpleText:='共有'+inttostr(MailSum)+'封邮件'
    else
      showmessage('没有邮件');
    for index := 1 to MailSum do
    begin
      IdMessage1.Clear;
      IdPOP31.RetrieveHeader(index,IdMessage1);//获取邮件头部信息
      MailItem:=lvmail.items.add;
      MailItem.Caption:=inttostr(index);
      MailItem.SubItems.Add((DecodeBase64(IdMessage1.Subject)));//邮件主题
      MailItem.SubItems.Add(IdMessage1.From.Address);//文件
      MailItem.SubItems.Add(FormatDateTime('yyyy-mm-dd hh:mm:ss',IdMessage1.Date));//时间
      MailItem.SubItems.Add(IntToStr(IdPOP31.RetrieveMsgSize(index) div 1024)+'K');//大小
      IdMessage1.Clear;
      IdPOP31.Retrieve(Index,IdMessage1);//获取邮件
      IdMessage1.MessageParts.CountParts;//获得邮件的分部分计算
      if IdMessage1.MessageParts.AttachmentCount >0 then
        MailItem.ImageIndex:= 5 //有附件
      else
        MailItem.ImageIndex:=4;
    end;
  end;
end;
procedure TFormMain.lvAttachDblClick(Sender: TObject);
var
Index:Integer;
begin
  Index:=StrToInt(lvAttach.ItemFocused.Caption);//这里隐藏额序列号
  if  sSaveDialog1.Execute then
  begin
  TIdAttachment(IdMessage1.MessageParts.Items[index]).SaveToFile((sSaveDialog1.FileName));
  end;
end;procedure TFormMain.lvMailDblClick(Sender: TObject);
var
 Index:integer;
 AttachItem:TListItem;
begin
MemoMail.Lines.Clear;
LVAttach.Items.Clear;
IdMessage1.Clear;
IdMessage1.ContentType:='Multipart/*';//邮件类型
sStatusBar1.SimpleText:='开始接收';
IdPOP31.Retrieve(LVmail.ItemIndex+1,IdMessage1);
sStatusBar1.SimpleText:='接收完毕';
memomail.Lines:=IdMessage1.Body;//邮件正文
 for Index:=0 to Pred(IdMessage1.MessageParts.Count) do
 begin
   if IdMessage1.MessageParts.Items[Index] is TIdAttachment then
   begin
   AttachItem:=lvAttach.Items.Add;
   AttachItem.Caption:=IntTostr(index);
   AttachItem.SubItems.Add(TIdAttachMent(IdMessage1.MessageParts.Items[Index]).FileName);
   end
   else if IdMessage1.MessageParts.Items[index] is TIdText then
   begin
   MemoMail.Lines.Clear;
   MemoMail.Lines.AddStrings(TIdText(IdMessage1.MessageParts.Items[Index]).Body);
   end;
 end;
end;procedure TFormMain.N6Click(Sender: TObject);
begin
  FormConfig.showmodal;//显示设置邮件服务器窗体
end;
end.现在主要有3个问题：
1，邮件乱码
2，为什么在接收邮件时程序出现假死
3，发邮件乱码的解决办法
希望大大们帮助解答