I just installed postfix 2.7.11 in Ubuntu server from source code. I do not use the ubuntu own one because I need the old version. I found a very interesting problem. Before, in both CentOS 5 and 6, I can build the source code without any problem. But, in Ubuntu server 12.04 is totally different. I got the following problems: dict_nis.c:173: error: undefined reference to 'yp_match' dict_nis.c:187: error: undefined reference to 'yp_match' dns_lookup.c:347: error: undefined reference to '__dn_expand' dns_lookup.c:218: error: undefined reference to '__res_search' dns_lookup.c:287: error: undefined reference to '__dn_expand' dns_lookup.c:498: error: undefined reference to '__dn_expand' dns_lookup.c:383: error: undefined reference to '__dn_expand' Yes, this reason is obviously. I just search related library and add it to the makefile. It works. The question is why? What is the difference between Ubuntu Server and CentOS? One possibility is gcc and ld version. Ubuntu server use different version of gcc and ld with CentOS. But I am not sure.