Hi,

rfc2045 has the following requirement:

 RFC> It should also be noted that, by definition, if a composite entity                                                           
 RFC> has a transfer-encoding value such as "7bit", but one of the enclosed                                                        
 RFC> entities has a less restrictive value such as "8bit", then either the                                                        
 RFC> outer "7bit" labelling is in error, because 8bit data are included,                                                          
 RFC> or the inner "8bit" labelling placed an unnecessarily high demand on                                                         
 RFC> the transport system because the actual included data were actually                                                          
 RFC> 7bit-safe.                                                                                                                   

but when gnus sends a multipart messages, it does not set the
content-transfer-encoding=8bit of the whole message when one of the
parts has 8bit (or content-transfer-encoding=binary when one of the
parts has binary CTE).

by default, the CTE, if omitted, is assumed to be 7bit (as stated in
the same RFC).

This message has a part with 8bit CTE, but gnus does not set the 8bit
CTE for the whole message.

Best,
v.