gnus-gcc-externalize-attachments

gnus-gcc-externalize-attachments is a variable defined in `gnus-msg.el'.
Its value is

nil

Documentation:
Should local-file attachments be included as external parts in Gcc copies?
If it is `all', attach files as external parts;
if a regexp and matches the Gcc group name, attach files as external parts;
if nil, attach files as normal parts.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.1 of Emacs.