Sendmail has these errors--Domain of sender address <root@time.com> does not exist

Does anyone has a clue of what is going on here? It was working few days ago. /etc/hosts looks ok, sendmail does restart without any errors, telnet is successful. I will be happy to send you guys any output required.

Diagnostic-Code: SMTP; 553 #5.1.8 Domain of sender address <root@tiger.time.com> does not exist

Domain of sender address <root@time.com> does not exist

[root@tiger mail]# /usr/lib/sendmail -Am -v tiger@time.com </dev/null
tiger@time.com... Connecting to sendmailtiger.time.com. via relay...
220 sendmailtiger.time.com ESMTP
>>> EHLO tiger.time.com
250-sendmailtiger.time.com
250-8BITMIME
250-SIZE 20971520
250 STARTTLS
>>> STARTTLS
220 Go ahead with TLS
>>> EHLO tiger.time.com
250-sendmailtiger.time.com
250-8BITMIME
250 SIZE 20971520
>>> MAIL From:<root@tiger.time.com>
553 #5.1.8 Domain of sender address <root@tiger.time.com> does not exist
/root/dead.letter... Saved message in /root/dead.letter
Closing connection to sendmailtiger.time.com.
>>> QUIT
221 sendmailtiger.time.com

Not quite sure what you are trying to do here, but lets assume that this is an Internet-facing server, not a sandbox.
If you are the owner of the domain time.com (unlikely?) you appear to have not registered sendmailtiger.time.com and tiger.time.com and you are therefore failing a reverse DNS lookup.
Eventally the Internet Police will block your IP.

Good luck.