ResolutionThe bounce message example:
Hi. This is the qmail-send program at hostname.tld.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.
Sorry, I couldn't find a mail exchanger or IP address. (#5.4.4)
This message means that Qmail failed to get the MX and A records for the 'destination_server'. In other words, the destination server is not resolved, 765.