in the past, I made an attempt to wrote a remove_attachment plugin. the first version had several bugs. I recently rewrote it with squirrelmail 1.4.15, and the code is much cleaner.
version 1.3 of the plugin, fixes a problem that adds the removal link as the default link
version 1.4 of the plugin, fixes problems with nested messages and global_variables = off
version 1.5 of the plugin, fixes problems with short_open_tags=off