Hi,
For Netscape Messaging Server migrations, reimplement customized plug-ins.
Since the iPlanet Messaging Server does not support messaging plug-ins, plug-in functionality will need to be redesigned and recoded using features of the new MTA.
The MTA has functions that handle the most common plug-in functions. See "Netscape Messaging Server 4.x MTA Regressions/Changes".
http://docs.iplanet.com/docs/manuals/messaging/ims50/mg/overview.htm#21133