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I'm sorry about the lack of details I'm going to give. My Linux knowledge is limited, but I'm happy to go find out more... Here's my problem:
We've recently had to move some servers on our network. They are in a new ip range. Everything seems to be ok. People can log on to our websites externally. We do have a problem sending email now, though. We have several qmail servers and a sendmail server. None of them seen to be able to be able to forward mail from other servers. For example we have a website that will email forgotten passwords. The system seems to think it successfully sends the details, but actually it fails to send them. I've tried Telneting from the websever to the mailserver. That works, but a normal message fails. Because we have moved our servers I think the mail servers must need to know the ipaddresses or machines that are allowed to send it mail to forward. Is this theory correct and how do I go about configuring these settings?
See if you have any hard coded server names or IP addresses.
For example the Smart Mail Relay line could have:
Where xxx.xxx.xxx was the old IP address. You'd want to change this from IP address to name and insure you could look up the name and get its IP address (via DNS or /etc/hosts for example). Failing that you could just hard code the new IP address of the destination relay.
Haven't worked with qmail but it likely has similar configs that need to be modified if you've hardcode IP addresses or can no longer look up host to ip mappings for some reason.
Check your /etc/resolv.conf to be sure the "nameservers" it specifies have your new IP ranges if the nameservers moved too.
Nothing. /etc/resolv.conf is read at the time of the lookup (assuming your /etc/nsswitch.conf says to use DNS).
Are you saying the old addresses ARE there or that there are NO addresses there? If the latter then it means you likely didn't have them before so they probably aren't your issue now. If the former make sure you delete the old addresses.
In /etc/resolv.conf are the old ip addresses. I will add the new ones and delete the old ones. Thank you for telling me about this - I would never have known. I will reply back when I have made the change and say if it was successful.
Check /etc/hosts on each of the systems and insure the IP addresses are updated there (especially for the the system itself). Make sure the system's entry is the first one after the one for 127.0.0.1 (localhost).