Hi I've got a ISPConfig/Centos5 server that has recently been running very happily. Unfortunately I have started to come across news that various people trying to send email to one of the domains on my server are having them returned with the message "Sorry, I couldn't find any host by that name. (#4.1.2) Despite repeated attempts, this message could not be delivered." BUT mail from other companies is arriving very happily. When my client first reported some emails not arriving, I checked my mail logs and cannot find any attempts by the other company's server to connect and deliver. (But did find frequent emails being received from that company up until the 10th June) I have checked my DNS settings using DIG. Everything seems in order. When checking the domain, an MX record was found. When digging the mx record, an 'A' record with the correct IP address is found. The PTR record for the IP address appears to be correctly set. Any ideas about what is going on?