our GWIA (2012 on SLES 11 SP2, dedicated for SMTP) is sending outgoing mail
to a relay (sendmail). In the logs I see several hundred "Send Failure: 450
Host down" per day.

I talked to the sendmail admin and he told me there is a setting
MaxDaemonChildren=15; I checked the GWIAs settings, which has SMTP send

My first question: I think increasing MaxDaemonChildren would not help in
this case. Or does GWIA open more than one connection per thread?

My second question: I'm a bit confused about the different GWIAs settings.
There is "Intervals to retry a defered message"; but there are also retry
settings in the "Optional Gateway settings" - do the latter play any role