[Exim] explicit defers in ACLs

right this minute, i'm looking at something that would be easy to do if i
could defer explicitly in an ACL to give a 4xx code. my reading of the
exim 4 docs suggests that this currently isn't possible.

have i read correctly? if so, i'd like to see an explicit defer condition
put on the wish list. if not, someone please explain what i've overlooked.

thanks,
  richard
--
Richard Welty
rwelty@???                                 Averill Park Networking
rwelty@???           Unix, Linux, IP Network Engineering, Security
rwelty@???                                     518-573-7592