Hallo,

| Notes: In Internet mail messages, the addr-spec in a Content-ID
| [MIME] or Message-ID [822] header is enclosed in angle brackets
| (<>).
....
| Some Examples
....
|  Content-ID: <foo4*foo1@bar.net>
-- RFC 2392, Abschnitt 2

...d.h. die Content-ID muss ein bestimmtes Format haben?

Alex