We recently started getting the following NDR:"You do not have permission to send to this recipient. For assistance, contact your system administrator. <mailserver.name.org #5.7.1 smtp;550 5.7.1 Unable to relay for recipient@wherever.comv>"What we know:- This is only occuring for a handful of outbound domains. - If the sender hits the resend button multiple times, the message eventually goes to the recipient successfully- We are not on any blacklists- If the sender's IP address is added into the mail server's relay table, the problem goes away. If they're taken back out, the problem returns. This, dispite the fact that the box to "Allow all computers which successfully authenticate to relay..." is checked.- Anonymous Access is enabled- We have flushed the DNS cache & rebooted the mail servers, & neither helped- The servers are up-to-date on patches & service packsThoughts? Ideas?

When adding the client IP to the allowed exceptions list it bypasses the credential check. since thats the only difference, id start with resetting the users password and having them resupply credentials to ensure thats not a factor. following that, id send a few test messages from outlook with logging enabled on the exchange server. read through the code to see what the difference is between the failed/successful attemptsMike Crowley: MCT, MCSE, MCTS, MCITP: Enterprise Administrator / Messaging Administrator

Hi,Whether this issue exists on all the users or few user?Please enable SMTP logging on the SMTP Virtual Server, select the Active log format as Microsoft IIS Log File Format. Then send the test email, locate the C:\WINDOWS\System32\LogFiles\SMTPSVC1 path to find the log file, and send it to me at v-allson@microsoft.comThanksAllen