Bugzilla

This is caused by the MIME part header:
```Content-Location:smil.xml```

If I remove this header, the mail is displayed correctly.

This header can be used to redirect cross-references in the content to other body parts.

On the one hand, the header here is wrong and meaningless, which is why it leads to the wrong presentation, but on the other hand, there is an explicit exception in the treatment:

[RFC 2557 - 8.3 Use of the Content-ID header and CID URLs](https://datatracker.ietf.org/doc/html/rfc2557#section-8.3)
| When URIs employing a CID (Content-ID) scheme as defined in [URL] and
| [MIDCID] are used to reference other body parts in an MHTML
| multipart/related structure, they MUST only be matched against
| Content-ID header values, and not against Content-Location header
| with CID: values. Thus, even though the following two headers are
| identical in meaning, only the Content-ID value will be matched, and
| the Content-Location value will be ignored.
| 
|    Content-ID: <foo@bar.net>
|    Content-Location: CID: foo@bar.net
| 
| Note: Content-IDs MUST be globally unique [MIME1]. It is thus not
| permitted to make them unique only within a message or within a
| single multipart/related structure.

The IMG references in the body should therefore not be affected.
Like e.g.:
```<IMG src="cid:tmobilespace.gif" width="350" height="30">```