*folder*, `folders': follow suit UNIX v10 Mail and BSD Mail (elo)..

*folder*, `folders': follow suit UNIX v10 Mail and BSD Mail (elo)..

UNIX v10 mail, and BSD Mail since 1982

  Author:     Kurt Shoens <kurt>
  AuthorDate: 1982-03-15 09:43:52 -0800
  Commit:     Kurt Shoens <kurt>
  CommitDate: 1982-03-15 09:43:52 -0800

      Included Eric's branch changes to remove vax and vmunix
      dependencies.

use the clear implementation

  +       if ((folder = value("folder")) == NOSTR)
  +               return(-1);
  +       if (*folder == '/')
  +               strcpy(name, folder);
  +       else
  +               sprintf(name, "%s/%s", homedir, folder);

as stated by elo in a follow-up to NetBSD Problem Report #54764.
This contradicts POSIX wording which says "unset or null".
Let us follow the implementations.