Why not add support for PRDR? Take a look at the (unfortunately expired) internet draft from Eric A. Hall:
SMTP Service Extension for Per-Recipient Data Responses (PRDR) It is supported by one MTA (MeTA1, see http://www.meta1.org/). -- ## List details at http://lists.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://wiki.exim.org/
