The following is a list of variables that influence how the mail is fetched. You would normally not need to set or change any of these variables.
mail-source-crash-boxmail-source-delete-incomingnil, delete incoming files after handling
them. If t, delete the files immediately, if
nil, never delete any files. If a positive number,
delete files older than number of days (the deletion will only
happen when receiving new mail). You may also set
mail-source-delete-incoming to nil
and call mail-source-delete-old-incoming from a
hook or interactively. mail-source-delete-incoming
defaults to 10 in alpha Gnusae and 2
in released Gnusae. See Gnus
Development.mail-source-delete-old-incoming-confirmnil, ask for confirmation before
deleting old incoming files. This variable only applies when
mail-source-delete-incoming is a positive
number.mail-source-ignore-errorsnil, ignore errors when reading mail from a
mail source.mail-source-directorymail-source-delete-incoming is nil or
a number.mail-source-incoming-file-prefixmail-source-delete-incoming is
nil or a number.mail-source-default-file-modesmail-source-movemail-programnil, name of program for fetching new mail. If
nil, movemail in
exec-directory.