I can't send email to one domain on my server. Email to all other domains works fine. The message I get back is:

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There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
#5.5.0 smtp;550 relaying to prohibited by administrator>
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I checked the logs of my local mail server and it's attempting to send the message, but is receiving the 550 back from my rackshack server.

There is NOTHING in /var/log/messages nor /usr/local/psa/var/log/maillog that indicates a problem...which is a problem in and of itself! Mail to other domains is logged.

I verified that this particular domain is listed in both /var/qmail/control/rcpthosts and /var/qmail/control/virtualdomains .

Everything appears normal in Plesk. I even tried enabling open relay, then re-enabling authentication.

I'm at a loss.

Dang this is frustrating.

I disabled the domain mail service for that domain, and verified that the domain disappeared from both rcpthosts and virtualdomains ... I then turned the domain mail service back on and verified that the domain appeared back in both those files.

STILL I get the same dang 550. How can this be?

Welp, whatever, it's working now.

THE SOLUTION:

Try all sorts of random junk until it works. If it still doesn't work, send an email to yourself via webmail. Keep trying these things until it eventually works. Make sure to properly ground yourself with an anti-static wristband. Oh, and make sure to over-react and curse a lot.

Could not hold myself back, had to reply to this post.

JAJAJA, thx for making me smile. Glad your way works, but not my style.