+.new
+Before Exim carries out a maildir delivery, it ensures that subdirectories
+called &_new_&, &_cur_&, and &_tmp_& exist in the delivery directory. If they
+do not exist, Exim tries to create them and any superior directories in their
+path, subject to the &%create_directory%& and &%create_file%& options. If the
+&%maildirfolder_create_regex%& option is set, and the regular expression it
+contains matches the delivery directory, Exim also ensures that a file called
+&_maildirfolder_& exists in the delivery directory. If a missing directory or
+&_maildirfolder_& file cannot be created, delivery is deferred.
+
+These features make it possible to use Exim to create all the necessary files
+and directories in a maildir mailbox, including subdirectories for maildir++
+folders. Consider this example:
+.code
+maildir_format = true
+directory = /var/mail/$local_part\
+ ${if eq{$local_part_suffix}{}{}\
+ {/.${substr_1:$local_part_suffix}}}
+maildirfolder_create_regex = /\.[^/]+$
+.endd
+If &$local_part_suffix$& is empty (there was no suffix for the local part),
+delivery is into a toplevel maildir with a name like &_/var/mail/pimbo_& (for
+the user called &'pimbo'&). The pattern in &%maildirfolder_create_regex%& does
+not match this name, so Exim will not look for or create
+&_/var/mail/pimbo/maildirfolder_&, though it will create
+&_/var/mail/pimbo/{cur,new,tmp}_& if necessary.
+
+However, if &$local_part_suffix$& contains &`-eximusers`& (for example),
+delivery is into the maildir++ folder &_/var/mail/pimbo/.eximusers_&, which
+does match &%maildirfolder_create_regex%&. In this case, Exim will create
+&_/var/mail/pimbo/.eximusers/maildirfolder_& as well as the three maildir
+directories &_/var/mail/pimbo/.eximusers/{cur,new,tmp}_&.
+
+&*Warning:*& Take care when setting &%maildirfolder_create_regex%& that it does
+not inadvertently match the toplevel maildir directory, because a
+&_maildirfolder_& file at top level would completely break quota calculations.
+.wen
+