在C＃中使用正则表达式匹配多行

I have the following text:

我有以下文字：

--------------030805090908050805080502
Content-Type: image/jpeg
Content-Transfer-Encoding: base64
Content-ID: <[email protected]>

/9j/4AAQSkZJRgABAgAAZABkAAD/7AARRHVja3kAAQAEAAAARgAA/+4ADkFkb2JlAGTAAAAA
/9j/4AAQSkZJRgABAgAAZABkAAD/7AARRHVja3kAAQAEAAAARgAA/+4ADkFkb2JlAGTAAAAA
QBQH/9k=
--------------030805090908050805080502
Content-Type: image/jpeg
Content-Transfer-Encoding: base64
Content-ID: <[email protected]>

/9j/4AAQSkZJRgABAgAAZABkAAD/7AARRHVja3kAAQAEAAAARgAA/+4ADkFkb2JlAGTAAAAA
/9j/4AAQSkZJRgABAgAAZABkAAD/7AARRHVja3kAAQAEAAAARgAA/+4ADkFkb2JlAGTAAAAA
juu41lRHFLufPCAID//Z
--------------030805090908050805080502--
--------