I have an Exchange 2003 server running on Server 2003. My company emails another company frequently. For the most part this is not a problem, but occasionally all the email that is being sent from my company does not get delivered to any user at the other company. This has happened 3 times and usually for a period of 2-3 days, then it works again. When the email will not go through, I get the following error: This message was created automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: user@othercompany.com SMTP error from remote mail server after MAIL FROM:SRS0=wrfFbf=5N=mycompany.com=myuser@mycompany.com: hostothercompany.com [ip address]: 550 5.7.1 Mailserver access requires prior approval for your address space.The other company says they have not changed settings and I say I have not changed settings. Thanks in advance for any help!

Hi,They use gray-listing to prevent spam what I can see from the message you received. With grey-listing your IP-address first needs to be listed in their approved list before you can send mail to them.Ask them to check their anti-spam solution.Regards,Johan blog: www.johanveldhuis.nl

Hi, For Greylisting, we should receive a temporary error (4XX). You can refer to following article regarding the Greylisting: http://www.greylisting.org/articles/whitepaper.shtml Regarding the issue, I suggest you have a look at the SMTP protocol log to check whether you can find further clues. Please also let me know whether you are able to send email to other domains. If the other domains are able to receive your email, I think you need to work with other company regarding the issue. Mike

Thank you for the response. Yes we are able to email all other domains except one other. I did find that we cannot email two domains and they are both handled by the same ISP. I will get in contact with the ISP asap and see if they can shed some light on the matter. SMTP logs do not give any further information regarding these emails.