I maintain a dozen or so SBS 2003 boxes. Very rarely, one of the users (from various servers) will forward me an NDR that looks like this:
<our_exchange_server_name> #5.7.1 smtp;554 5.7.1 <external_email_address>: Relay access denied>
In every case, the recipient's email address (external) is someone we have emailed before. These emails will go through most of the time, but sometimes not. Since they go through most of the time, you'd think it's not an issue on our end or their end, but some kind of temporary issue.
I've been reading through MS KBs and answers here on EE, but no resolution yet.
I have verified that my FQDN is correct in the SMTP virtual server.
I'm not sure where exactly to look to see exactly what is going wrong with these individual emails that are having trouble. Today, I have had a user at one organization that has been unable to email the external recipient all day, but she was able to email the external recipient yesterday.
Where do I start in the troubleshooting process on this one?