I run Exchange 2003 on our server and it's been running well for months. About an hour ago we stopped having the ability to send external emails to most domains. I can send an email to gmail but not to hotmail. No software or server upgrades were preformed on our server.
The error replay we're getting is..
There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<xxx.xxx.intranet #5.5.0 smtp;550 OU-001 (SNT0-MC4-F46) Unfortunately, messages from 188.8.131.52 weren't sent. Please contact your Internet service provider since part of their network is on our block list. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors
I checked the blacklist sites and we were listed on one which I had them delist us. I've also called our service provider (Verizon FIOS) and I'm being told it has nothing to do with them.
Any guidance would be greatly appreciated.