Thanks Zhang.
Which log file do you need - this is mail.log:
When mailgun forwards to inbound.hong2.com ->
Jun 13 08:04:31 x postfix/smtpd[9874]: connect from mail-s65.mailgun.info[184.173.153.193]
Jun 13 08:04:31 x postfix/smtpd[9874]: NOQUEUE: reject: RCPT from mail-s65.mailgun.info[184.173.153.193]: 550 5.1.0 <bounce+f3ca76.809f-jeff=inbound.hong2.com@hong2.com>: Sender address rejected: User unknown in virtual mailbox table; from=<bounce+f3ca76.809f-jeff=inbound.hong2.com@hong2.com> to=<jeff@inbound.hong2.com> proto=ESMTP helo=<mail-s65.mailgun.info>
Jun 13 08:04:31 x postfix/smtpd[9874]: disconnect from mail-s65.mailgun.info[184.173.153.193]
When I send from gmail direct to jeff@inbound.hong2.com:
Jun 13 08:03:44 x postfix/smtpd[9896]: connect from x.hong2.com[127.0.0.1]
Jun 13 08:03:44 x postfix/smtpd[9896]: 7BFF325262: client=x.hong2.com[127.0.0.1]
Jun 13 08:03:44 x postfix/cleanup[9888]: 7BFF325262: message-id=<CADB8sxQZ5VLhmdfhSA7T=qRfAFWGGnJY1a4N_5hvKvmC9P4K0Q@mail.gmail.com>
Jun 13 08:03:44 x postfix/qmgr[8762]: 7BFF325262: from=<bounce+999672.a2136-jeff=inbound.hong2.com@geogram.co>, size=3648, nrcpt=1 (queue active)
Jun 13 08:03:44 x postfix/smtpd[9896]: disconnect from x.hong2.com[127.0.0.1]
Jun 13 08:03:44 x amavis[1268]: (01268-13) Passed CLEAN, LOCAL [184.173.153.193] [209.85.220.52] <bounce+999672.a2136-jeff=inbound.hong2.com@geogram.co> -> <jeff@hong2.com>, Message-ID: <CADB8sxQZ5VLhmdfhSA7T=qRfAFWGGnJY1a4N_5hvKvmC9P4K0Q@mail.gmail.com>, mail_id: apjQtQJf+ka3, Hits: 0, size: 3030, queued_as: 7BFF325262, dkim_id=@geogram.co,jeff=newscloud.com@geogram.co, 4867 ms
Jun 13 08:03:44 x postfix/smtp[9893]: 4AA8925237: to=<jeff@hong2.com>, relay=127.0.0.1[127.0.0.1]:10024, delay=6.6, delays=1.5/0.01/0.16/4.9, dsn=2.0.0, status=sent (250 2.0.0 from MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as 7BFF325262)
Jun 13 08:03:44 x postfix/qmgr[8762]: 4AA8925237: removed
Jun 13 08:03:44 x postfix/pipe[9897]: 7BFF325262: to=<jeff@hong2.com>, relay=dovecot, delay=0.15, delays=0.01/0.02/0/0.12, dsn=2.0.0, status=sent (delivered via dovecot service)
Jun 13 08:03:44 x postfix/qmgr[8762]: 7BFF325262: removed