Determines seconds to wait before trying to relay message.

An Integer value.  

object.IdleWait [= value]

The IdleWait Property syntax has these parts:

IdleWait property determines how many seconds wodSmtpServer will wait before it actually tries to perform next try to relay the message. Since we don't want to freeze server with (failed?) attempts to relay messages, between all tries there's some timer specified by IdleWait property.

So, once you add the relay, it will wait few seconds. If relay fails (because destination server is unreachable, for example), and component tries to send message to secondary mail exchanger, it will wait again same number of seconds etc..