为什么 body 和 sender 都是空的？

Question

我正在使用此代码从服务器读取电子邮件，它可以工作，除了 Sender.Address 和 Body.Text 是空的，为什么会这样？。代码如下：

var
  MsgCount : Integer;
  i        : Integer;
  FMailMessage :  TIdMessage;
begin
  Memo1.Lines.Clear;
  //The IdPop31 is on the form so it is constructing when the
  //form is created and so is Memo1.
  IdPOP31.Host      := 'server.com'; //Setting the HostName;
  IdPOP31.Username  := 'email@server.com';//Setting UserName;
  IdPOP31.Password  := 'xxxxxx';//Setting Password;
  IdPOP31.Port      := 110;//Setting Port;

  try
    IdPOP31.Connect();
    //Getting the number of the messages that server has.
    MsgCount := IdPOP31.CheckMessages;
    for i:= 1 to Pred(MsgCount) do
    begin
      try
        FMailMessage := TIdMessage.Create(nil);
        IdPOP31.Retrieve(i,FMailMessage);
        Memo1.Lines.Add('=================================================');
        Memo1.Lines.Add(FMailMessage.From.Address);
        Memo1.Lines.Add(FMailMessage.Recipients.EMailAddresses);
        Memo1.Lines.Add(FMailMessage.Subject);
        Memo1.Lines.Add(FMailMessage.Sender.Address);
        Memo1.Lines.Add(FMailMessage.Body.Text);
        Memo1.Lines.Add('=================================================');
      finally
        FMailMessage.Free;
      end;
    end;
  finally
    IdPOP31.Disconnect;
  end;
end;

Answer 1

仅当电子邮件具有顶级 Sender 标头时才会填充 TIdMessage.Sender，这种情况很少见。通常，发件人位于 From 标头中。

正文内容将存储在TIdMessage.Body 或TIdMessage.MessageParts 中，具体取决于电子邮件的编码方式。通常，多件电子邮件（例如使用 MIME 编码的电子邮件，尤其是包含附件的电子邮件）将使用 TIdMessage.MessageParts，而简单电子邮件（例如纯文本电子邮件）将使用 TIdMessage.Body。因此，您需要根据需要检查两者。

例如：

var
  MsgCount, I: Integer;
  FMailMessage: TIdMessage;
  Body: TStrings;

  function FindTextBody(AParent: Integer): TStrings;
  var
    J: integer;
    Part: TIdMessagePart;
  begin
    Result := nil;
    // MIME parts are ordered from least complex to most complex, and can be nested,
    // so loop backwards through the parts, recursing through nested levels as needed...
    for J := Pred(FMailMessage.MessageParts.Count) downto (AParent+1) do
    begin
      Part := FMailMessage.MessageParts[J];
      if Part.ParentPart = AParent then
      begin
        if IsHeaderMediaType(Part.ContentType, 'multipart') then
        begin
          Result := FindTextBody(Part.Index);
          if Result <> nil then Exit;
        end
        else if IsHeaderMediaType(Part.ContentType, 'text') then
        begin
          Result := (Part as TIdText).Body;
          Exit;
        end;
      end;
    end;
  end;

begin
  Memo1.Lines.Clear;
  //The IdPop31 is on the form so it is constructing when the
  //form is created and so is Memo1.
  IdPOP31.Host      := 'server.com'; //Setting the HostName;
  IdPOP31.Username  := 'email@server.com';//Setting UserName;
  IdPOP31.Password  := 'xxxxxx';//Setting Password;
  IdPOP31.Port      := 110;//Setting Port;
  try
    IdPOP31.Connect();
    //Getting the number of the messages that server has.
    MsgCount := IdPOP31.CheckMessages;
    for I := 1 to Pred(MsgCount) do
    begin
      FMailMessage := TIdMessage.Create(nil);
      try
        IdPOP31.Retrieve(I, FMailMessage);
        Memo1.Lines.Add('=================================================');
        Memo1.Lines.Add(FMailMessage.From.Address);
        Memo1.Lines.Add(FMailMessage.Recipients.EMailAddresses);
        Memo1.Lines.Add(FMailMessage.Subject);
        Memo1.Lines.Add(FMailMessage.Sender.Address);
        if FMailMessage.MessageParts.Count > 0 then
          Body := FindTextBody(-1)
        else
          Body := FMailMessage.Body;
        if Body <> nil then
          Memo1.Lines.Add(Body.Text);
        Memo1.Lines.Add('=================================================');
      finally
        FMailMessage.Free;
      end;
    end;
  finally
    IdPOP31.Disconnect;
  end;
end;