[SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] [X] [Z] X configuration file command  x delivery agent flag  X delivery agent flag  X-Authentication-Warning: header line  2nd  X.400 addresses  2nd  X400-Received: header line  XDEBUG compile-time macro  xdelay= equate (syslog output)  xf files      separate directory for  XX_DQUOTE_XX (quotation marks)  XYZ text expression (access database)