nnmail-split-lowercase-expanded

nnmail-split-lowercase-expanded is a variable defined in `nnmail.el'.
Its value is

t

Documentation:
Whether to lowercase expanded entries (i.e. \N) when splitting mails.
This avoids the creation of multiple groups when users send to an address
using different case (i.e. mailing-list@domain vs Mailing-List@Domain).

You can customize this variable.

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