Please don't feel its just another thread on this topic I did search forums and stuffs, learned a bit but still its not clear why a mail is rejected saying sender address rejected, and domain not found. It is a local account in my server and a real one.

Jan 19 10:27:46 postfix/smtpd[24022]: 6A6461488403: client=localhost.localdomain[127.0.0.1]
Jan 19 10:27:46 postfix/cleanup[24161]: 6A6461488403: message-id=<725609724.510040.1295429086293.JavaMail.root@x xxx>
Jan 19 10:27:46 postfix/qmgr[19098]: 6A6461488403: from=<myacc@domain>, size=38495, nrcpt=1 (queue active)
Jan 19 10:27:46 amavis[21010]: (21010-01-34) FWD via SMTP: <myacc@domain> -> <acco@domain>,BODY=7BIT 250 2.0.0 Ok, id=21010-01-34, from MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as 6A6461488403
Jan 19 10:27:46 amavis[21010]: (21010-01-34) Passed CLEAN, [xx.xx.xx.xx] <myacc@domain> -> <acco@domain>, Message-ID: <725609724.510040.1295429086293.JavaMail.root@xxxx x>, mail_id: xwItztyOQ6jl, Hits: -6.899, size: 38056, queued_as: 6A6461488403, 904 ms
Jan 19 10:27:46 postfix/smtp[24125]: 51BC4148840F: to=<acco@domain>, relay=127.0.0.1[127.0.0.1]:10024, conn_use=34, delay=180, delays=0.01/179/0/0.91, dsn=2.0.0, status=sent (250 2.0.0 Ok, id=21010-01-34, from MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as 6A6461488403)
Jan 19 10:27:51 postfix/smtp[19061]: 6A6461488403: host mx.domain.com[xxx.xxxx.xxx.xx] said: 450 <myacc@domain>: Sender address rejected: Domain not found; [id:B7/3F-12863-39EA63D4] (in reply to RCPT TO command)

Reply to my 'RCPT TO' message as part of smtp ack is returned with the destination server saying 'sender address rejected and domain not found'. I understand this sender address is my acc and how does it end up in that conclusion?

My acc is not an external account. I don't think there is a dns problem since mail delivery is normal with other accounts. And my domain is properly resolving with proper MX and A records.

Can anyone guide me here?