How to bypass this error : admin@ - (bad address syntax)

How to bypass this error?

My maillog file :

Jan  5 15:39:42 server postfix/smtpd[23815]: connect from unknown[116.249.127.226]
Jan  5 15:39:53 server postfix/smtpd[23815]: warning: unknown[116.249.127.226]: SASL LOGIN authentication failed: UGFzc3dvcmQ6
Jan  5 15:39:53 server postfix/smtpd[23815]: lost connection after AUTH from unknown[116.249.127.226]
Jan  5 15:39:53 server postfix/smtpd[23815]: disconnect from unknown[116.249.127.226]
Jan  5 15:39:54 server postfix/smtpd[23851]: warning: 116.249.127.226: hostname 226.127.249.116.broad.km.yn.dynamic.163data.com.cn verification failed: Name or service not known
Jan  5 15:39:54 server postfix/smtpd[23851]: connect from unknown[116.249.127.226]
Jan  5 15:39:56 server postfix/qmgr[14430]: DF2971CC035A: from=<root@myserver.net>, size=38964, nrcpt=1 (queue active)
Jan  5 15:39:56 server postfix/error[24755]: DF2971CC035A: to=<admin@>, relay=none, delay=319790, delays=319790/0.01/0/0.05, dsn=4.1.3, status=SOFTBOUNCE (bad address syntax)
Jan  5 15:40:02 server postfix/pickup[19587]: 8B9361CC1E29: uid=0 from=<root>

Make sure you've mentioned full email address while creating a domain account. List all the accounts under the user account and see if you forgot to mention the full email. There should be a validation for the email field but it takes whatever you input. Messages from root will by default go to this account.