MTA = mail transport agent -or- message transfer agent
Applications like kmail, outlook express, etc... are configured to connect to MTA's (typically ISP's outbound mail server) for delivery of e-mail when you select the "send" button. Also, it's the MTA that issues the "relay denied" based on how its configured. Typically, ISP's configure their outbound MTA to only accept connections (relay) from customers on their network. But they can also reject the connection if the sending application (like kmail) announces its FQDN (fully qualified domain name) incorrectly (like hostname.mydomain.com instead of hostname.myisp.com).
On the other side of the coin - the file resolv.conf, configures your systems resolver libraries. Resolver libs are used by your system for name lookups (like www.yahoo.com
). If your systems resovler libs were incorrect, then you should see an error like "hostname not found" for ANY application trying to access the internet, NOT just kmail. So if you are not getting "hostname not found" type of errors when you use a program like a web browser, then I would think your resolv.conf file is configured to use the proper name servers.
A couple of things to check:
1) Is kmail configured to use the proper outbound mail server (MTA)? like: mail.myisp.net
2) Can the FQDN of your outbound mail server (mail.myisp.net) be looked up using DNS. i.e. nslookup mail.myisp.net This would verify your resolv.conf file is properly configured.
3) Is there a firewall possibly blocking access to your outbound mail server?