[Juu8888]

I had the same problem with Ubuntu 12.04 and postfix 2.9.3 with vda-patch 2.9.1

gcc -Wmissing-prototypes -Wformat -DDEBIAN -DMAX_DYNAMIC_MAPS -DHAS_PCRE -DHAS_LDAP -DHAS_SQLITE -DMYORIGIN_FROM_FILE -DNO_NIS -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -DHAS_CDB -DHAS_MYSQL -I/usr/include/mysql -DHAS_PGSQL -I/usr/include/postgresql -DHAS_SQLITE -I/usr/include -DHAS_SSL -I/usr/include/openssl -DUSE_SASL_AUTH -I/usr/include/sasl -DUSE_CYRUS_SASL -DUSE_TLS  -O2 -I. -I../../include -DLINUX3 -o smtpd smtpd.o smtpd_token.o smtpd_check.o smtpd_chat.o smtpd_state.o smtpd_peer.o smtpd_sasl_proto.o smtpd_sasl_glue.o smtpd_proxy.o smtpd_xforward.o smtpd_dsn_fix.o smtpd_milter.o smtpd_resolve.o smtpd_expand.o ../../lib/libmaster.a ../../lib/libtls.a ../../lib/libdns.a ../../lib/libxsasl.a ../../lib/libmilter.a ../../lib/libglobal.a ../../lib/libutil.a -lssl -lcrypto -lsasl2 -lpthread -L/usr/src/postfix-2.9.3/debian -ldb
../../lib/libdns.a: undefined reference to `__res_search'
../../lib/libdns.a: undefined reference to `__dn_expand'
collect2: ld gab 1 als Ende-Status zurück
make: *** [smtpd] Fehler 1

The reason of this error: missing -lresolv

I found a problem in Postfix makedefs file. Let's check the source:

Linux.3*)   SYSTYPE=LINUX3
            if [ -f /usr/include/db.h ]
            then
                : we are all set
            elif [ -f /usr/include/db/db.h ]
            then
                CCARGS="$CCARGS -I/usr/include/db"
            else
                # On a properly installed system, Postfix builds
                # by including <db.h> and by linking with -ldb
                echo "No <db.h> include file found." 1>&2
                echo "Install the appropriate db*-devel package first." 1>&2
                echo "See the RELEASE_NOTES file for more information." 1>&2
                exit 1
            fi
            SYSLIBS="-ldb"
            SEARCHDIRS=$(${CC-gcc} -print-search-dirs 2>/dev/null |
                    sed -n '/^libraries: =/s/libraries: =//p' |
                    sed -e 's/:/\n/g' | xargs -n1 readlink -f |
                    grep -v 'gcc\|/[0-9.]\+$' | sort -u)
            if [ -z "$SEARCHDIRS" ]; then
                    SEARCHDIRS="/usr/lib64 /lib64 /usr/lib /lib /usr/lib/i386-linux-gnu"
            fi
            for name in nsl resolv
            do
                for lib in $SEARCHDIRS
                do
                    test -e $lib/lib$name.a -o -e $lib/lib$name.so && {
                        SYSLIBS="$SYSLIBS -l$name"
                        break
                    }
                done
            done
            ;;

The explanation:

gcc -print-search-dirs | sed -n '/^libraries: =/s/libraries: =//p' didn't work for me, because i have Ubuntu in german language.

The gcc -print-search-dirs output is "Bibliotheken", german word of "libraries".

After changing the sed command the SYSLIBS variable filled in correctly and Postfix compiles fine.