Question : Smtp Error - sorry, no mailbox here by that name. (#5.7.17) when sending to certain domains

Hello, I'm having some trouble sending emails to certain domains:  The message I receive is "sorry, no mailbox here by that name. (#5.7.17)".  This error is constant no matter what individual user attempts to send, and only to certain domains.  I can email the user from other domains, such as a Gmail account, or yahoo, but not from our domain.  98% of our email functions normally with little or no issues, so i'm a little stumped.  Suggestions?  So far, i have:  Run a DNS Report from dnsstuff.com, which seem to pass, and our MX Records seem intact.  We DO use Postini for  Spam Filtering, and i have my suspicions that there may be an issue there... but their tests generate no failures.  So.. as for as testing goes everything passes.  I'm stumped.  My only thought from other posts is that perhaps we're being blocked for some reason..  Thoughts?  

Answer : Smtp Error - sorry, no mailbox here by that name. (#5.7.17) when sending to certain domains

Please have a read through my FAQ about problems sending emails to certain domains and chek that your environment is setup properly.  Once checked and any changes made - please try again to send and report back on what happens.

Alan

http://www.it-eye.co.uk/faqs/readQuestion.php?qid=2