用IdMessage读取eml文件的时候，body的内容为：This is a multi-part message.

解决办法：

uses IdText;

for j := IdMessage.MessageParts.Count-1 downto 0 do
begin
if (IdMessage.MessageParts[j] is TIdText) and
(IdMessage.MessageParts[j].ContentType = 'text/html') then
begin
memo1.text := (IdMessage.MessageParts[j] as
TIdText).Body.Text;
Break;
end;
end;