Re: several messages

> The current value of the default is a 60 second timeout. Perhaps
> reducing this to, say, 30 would help in some cases?

I suspect you may have missed a subtle bit which hasn't been explicitly
mentioned, just eluded to ...

With the correct setup of firewalls and old O/S code, the effect is that the
callback generates a "host unreachable" which causes the O/S to close all
calls to that host -- including the SMTP call !

It's not just the brain dead PC problem of accepting but not replying :-(