Hi, Two possibilities I can think of: a) Their mail server is mis-configured (always a possibility I suppose) b) The mail you are attempting to deliver is not destined for @domain.com -or- purports to be from @domain.com but the remote server does not have your host as an acceptable source of mail from @domain.com (the error message is basically saying that relay is prohibited. Relaying is the process of sending mail not destined for your domain through your mail server) HTH Cheers Ken : -----Original Message----- : From: thelist-bounces at lists.evolt.org [mailto:thelist-bounces at lists.evolt.org] On : Subject: [thelist] Emails not going out IIS 5 vs. Exchange Server 5.5 : : I'm getting this Event ID warning in my system logs of my web server: : : Message delivery to the remote domain 'domain.com' failed. The error : message is 'An SMTP protocol error occurred. : '. The SMTP verb which caused the error is 'RCPT'. The response from the : remote server is '550 Relaying is prohibited : : Source: smtpsvc : Event ID: 4001 : : Do you have any clue?