Apparently the libicu upstream has deprecated use of icu-config and recommends pkg-config instead. Debian has recently decided to stop shipping icu-config for obscure distro related reasons. The Debian libicu maintainer suggests this as an alternative (and it works here):
--- postfix-3.3.2.orig/makedefs +++ postfix-3.3.2/makedefs @@ -802,8 +802,8 @@ esac # case "$CCARGS" in *-DNO_EAI*) CCARGS="$CCARGS "'-DDEF_SMTPUTF8_ENABLE=\"no\"';; - *) icu_cppflags=`(icu-config --cppflags) 2>/dev/null` && { - icu_ldflags=`(icu-config --ldflags) 2>/dev/null` && { + *) icu_cppflags=`(pkg-config --cflags icu-i18n) 2>/dev/null` && { + icu_ldflags=`(pkg-config --libs icu-i18n) 2>/dev/null` && { trap 'rm -f makedefs.test makedefs.test.[co]' 1 2 3 15 cat >makedefs.test.c <<'EOF' #include <unicode/uidna.h> It does bring in a new requirement for pkg-config. I've no idea how portable that is. Assuming this approach is acceptable, you might want to consider this for 3.4. Scott K