Re: After a 450, queue or try next MX?

At 11:01 -0400 on 08/30/2006, Michael Kenny wrote about After a 450, 
queue or try next MX?:
> When I contacted the admin at the recipients domain he asserted that 
> my mail server was misconfigured, and that we should be retying. 
> While I'm not going to say that is not the case, I'm trying to 
> figure out first what it is that should happen here.
And I assert that HIS MX Server#2 is misconfigured. As a MX it should 
be willing to accept (and pass onto MX#1) any email passed to it 
(although I'd be willing to allow it to send a "550-Drop Dead - I 
don't want to talk to you" response AFTER it tries to connect to MX#1 
as a test it is up and willing to accept valid email) instead of 
sending a blow-off reply.
Lets look at the scenario with an inoperative MX#1 (instead of the 
"Go to MX#2 after MX#1's 45x" scenario). I try MX#1, fail to connect, 
so follow the MX Chain to MX#2 only to get blown off due to it not 
being configured as a valid fall-back MX server to MX#1. MX#2 should 
ALSO issue the 45x (unless as suggested above it can talk to MX#1 and 
thus assume that it is being tried WITHOUT first trying MX#1 [which 
is NOT a 100% bullet-proof assumption since the problem triggering a 
valid fall-back COULD be a connectivity problem between sender ISP 
and MX#1 while sender ISP can still connect to MX#2 due to using a 
different path - the whole idea of having separate locations for your 
MXs]).