mail-source-delete-old-incoming-confirm

mail-source-delete-old-incoming-confirm is a variable defined in `mail-source.el'.
Its value is

nil

Documentation:
If non-nil, ask for confirmation before deleting old incoming files.
This variable only applies when `mail-source-delete-incoming' is a positive
number.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.2 of Emacs.