Our domain started receiving this error today and only lets about 20% of e-mails throughRecent changes:Symantec Endpoint Protection client uninstalledPossible Windows Updates installedExchange Authentication - Basic Authentication (plain text enabled) was enabled for a couple of days. Now its disabled.All Default Microsoft Exchange services are running. There is few Exchange services not running, but these are not listed as default.I have tried restarting the server. cant think of anything else that was changed recently. This is the error that comes back to those who try to send us e-mailSorry, we were unable to deliver your message to the following address.<*****@arcelectronics.com>:Remote host said: 550 No Such User Here [RCPT_TO]or gmail's version: @arcelectronics.com Technical details of permanent failure:Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 No Such User Here (state 14). or in russian: м SMTP. мм м.<mail.pec.spb.ru #5.5.0 smtp;550 No Such User Here>Our setupWindows Server 2003 SBS / Exchange 2003We are using Barracuda / SpamHaus RBLThis applies to at least 3 of our users and these users have been receiving mail previously with no problems. These users do exist in the Active Directory as well as Exchange.Looking through Event Viewer I see a few error with MsExchangeTransport / SMTP Protocol EventID 7010 such asThis is an SMTP protocol log for virtual server ID 1, connection #174. The client at "217.25.227.95" sent a "helo" command, and the SMTP server responded with "501 5.5.4 Invalid Address ". The full command sent was "helo .mshome.net". This will probably cause the connection to fail. However most of those according to blacklists searches are coming from spammers or virus spreadersI also have a lot of DNS events 6702 (DNS server has updated its own host (A) records. In order to ensure that its DS-integrated peer DNS servers are able to replicate with this server, an attempt was made to update them with the new records through dynamic update. An error was encountered during this update, the record data is the error code. If this DNS server does not have any DS-integrated peers, then this error should be ignored. )There is only one 1 AD in this domain and its not replicating to any others. So im ignoring this.Restarting the server temporarily fixes this, thats not an aceptable solution however. the problemi s happening more and more often every day. d3v

On Thu, 15 Apr 2010 15:29:24 +0000, d3vlabs wrote:>Our domain started receiving this error today and only lets about 20% of e-mails through[ snip ]> Remote host said: 550 No Such User Here [RCPT_TO]That's not the status code an Exchange 2003 server would send if itwere perfroming recipient validation. There's something else, eitheron your server or between your server and the sender's server, that'ssending that status.Exchange would have sent the status cose and an extended status code:550 5.2.1 [ snip ]>Windows Server 2003 SBS / Exchange 2003We are using BarracudaVerify that the Barracuda is (or isn't) doing recipient validation. Ifthere's a SMTP protocol log you should check to see if that 550 statusis generated by thiat device.You can also check the SMTP protocl log on your Exchange server toverify what status codes are being returned when a recipient doesn'texist. If your Barracuda isn't doing the recipient validation I'd besurprised. ---Rich MatheisenMCSE+I, Exchange MVP--- Rich Matheisen MCSE+I, Exchange MVP