Your message was undeliverable due to the following reason:
Your message could not be delivered because the destination computer was
unreachable within the allowed queue period. The amount of time
a message is queued before it is returned depends on local configura-
Most likely there is a network problem that prevented delivery, but
it is also possible that the computer is turned off, or does not
have a mail system running right now.
Your message was not delivered within 8 days:
Mail server 18.104.22.168 is not responding.