We've been having this problem for a while, email sends fine to 90% of our clients however for a small selection the email won't leave the mailbox on any computer in the office, clients are also having problems on different domains to different email accounts I get the following error in Apple Mail, along with the rest of my clients using other mail programs. "Cannot send message using the server xxx Verify that you have addressed this message correctly. Check your SMTP server settings in Mail preferences and very any advanced settings with your system administrator" Anyone have any idea why we can't send to certain domains? My main question is why isn't the email leaving my mail account? What's causing it to not even leave? I don't get a bounce back or anything on the log as it won't connect to the server. Any help would be appreciated.