[exim] Queue life for 5xx + Connection errors

Good afternoon,

I have a bit of brain freeze I could use a jab in the right direction
with.

If Exim tries to deliver a message to a remote server and gets a 5xx
code back, say 550 no such user, am I right in thinking the message
should fail right away with an NDR, not remain on the queue being
re-tried?

More sticky, if a remote server refuses connections from Exim - say it
is firewalling off the connecting ip, should that fail at once or stay
on the queue for x hours?

I'm sure in the first case it should fail at once, and in the second
retry as the connection error could be transient, but I'd like to know
for sure before I start troubleshooting.

Ron