Message contains invalid header

[Marten Lehmann]

Hi,

>     case IMAP_MESSAGE_BADHEADER:
>         prot_printf(pout, "554 5.6.0 Message contains invalid header\r\n");
>         break;

what can I do to fix these headers? I have one message (which appears to 
be spam, but that is not the point), where I cannot find any problem. No 
8bit characters, no empty message-id header, what else could be wrong 
with it?

Regards
Marten