If the first mx record ( in mx 10 mail.scubaont.com) does not answer, or returns an invalid response
Any SMTP answer from an MX
At that point as I understand it the mail should be rerouted by the mail server that sent the mail
no, mail routing for that msg is terminated with the "550 unknown user" response.
What happens next is that the delivering MTA that has accepted the msg but receives the 550, will create a new message from mailer-daemon and try to send that new msg back to the envelope sender.
Note that this new msg is not necessarily identical to the original message. eg, in IMGate, I truncate the mailer-daemon msg so that is contains only the first 2 KB of the original message, which is sufficient for the sender to identify the msg whose delivery failed.
why? imagine a spammer sending us 1000's of 1 MB msgs with forged, but real sender names. I can't tell the msgs are forged, but my 1000's of mailer-daemon msgs will be max 2 KB each rather than 1 MB, greatly reducing the burden on my system, and greatly reducing the "attack" on the forged sender victim to whom I will will bouncing the msgs.
through to the second mx record on file and see if it gets a valid response from that server. Currently its not getting to the second MX record in the list.
It never will.
Is what I have above correct?
no, the 5xx returned by any MX will terminate the MX algorithm, aka mail delivery attempts or any other mail routing, for that msg. GAMEOVER
Len
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