email status=sent but not received by recipient

I set up a user from another domain (a sister company) to relay email through my local Postfix server. I added his email address to the sender_access file and it seemed to be working with several test emails we sent to local receipients and my gmail account.  A few hours later, however, he sent an email to a contact and this email never arrived. The log indicates the following:

May 6 20:51:51 mail postfix/smtp[13129]: E09A9EB54D: to<>,, delay=12, status=sent (250 Thanks)

To me this means that the message was handed off to the receiving server correct? Subsequent emails sent to this same person have also not been received.  The domain he is sending from is not a virtual domain on the server, he is strictly using my server as a relay all I did was add his address to the sender_access file.

If the remote server was rejecting the email for some reason wouldn't there be an error message?

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bevhostConnect With a Mentor Commented:
The remote server could be sending the mail to /dev/null without notice.
Assuming your server is looking up the XMX record for the recipients domain,
(rather than forwarding to some smarthost),
then it has been received by the receipients mail server and the recipient should follow this up himself.

Adding users to the sender_access is not such a good idea as anyone could use this.
I use SMTP-AUTH so that the user must specify a password.

Perhaps the senders domain has an SPF record.  See
dxhahnAuthor Commented:
I was mainly looking for confirmation that the log entry indicates a successful smtp delivery of the message, which I think is the case. I have not been able to reproduce the problem, but it also has not happened again, so I'm going to consider the issue closed unless I get some more information.  I'm aware of the problems with sender_access, and our new server does use SMTP Authentication. Thanks for your response
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