printing problem after mails working!

[Steven Chen_1]

I hope hp guru can give me some help:

In order to have mail working, I append /etc/hosts as:
xxx.xxx.xxx.xxx server server.domain.com
(server.domain.com is added).
Then my hp network printer is not working with error messages as follows:

1) from sam
fails to open any related printer menu. It says: "Error: could not contact host "server_name". Make sure the hostname is correct.

2) from /var/adm/lp
"hpnpf: unknown host printer_name"
note: printer_name is listed in /etc/hosts.

Before the mail related files change, printing is functioning well.

What should be done then?

Thanks a lot,

Steven