rmail-movemail-variant-in-use

rmail-movemail-variant-in-use is a variable defined in `rmail.el'.
Its value is

emacs

Documentation:
The movemail variant currently in use. Known variants are:

`emacs' Means any implementation, compatible with the native Emacs one.
This is the default;
`mailutils' Means GNU mailutils implementation, capable of handling full
mail URLs as the source mailbox.