smtp transports hanging after 4xx responce?

[Eugene Crosser <crosser@online.ru>]

Since I installed (some clone of) s18, I noticed that queue gets stuck
to a particular host.  Investigation show that there is a bunch smtp
transport instances in the status "running now" that are holding the
queue.  These instances do not have open connection, and in the log
they have reported "(closed SMTP channel - after delivery failure)"
(after they have got some 4xx responce).  Apparently, these instances
forgot to report to the scheduler that they finished processing mail
to the domain.  Another strange thing is that these processes consumed
much CPU (3 min as opposed to usual 1 sec).

Any thoughts?

Eugene