Unable to send mails to specific domain, mails stored in queue in exchnage server 2007
451 4.4.0 primary target ip address responded with 421 4.4.1 connection timed out. Attempted failver to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to alternate hosts.
Action taken :
Ip was blacklisted and spoke to isp and cleared.
Mx record found
Unable to send emails to only specific domain and able to receive mails.