diff -urNp syslog-ng-3.32.1-orig/configure.ac syslog-ng-3.32.1-dwok/configure.ac
--- syslog-ng-3.32.1-orig/configure.ac	2021-06-26 18:13:53.394483375 +0200
+++ syslog-ng-3.32.1-dwok/configure.ac	2021-06-26 18:12:58.985595602 +0200
@@ -1278,9 +1278,24 @@ if test "x$enable_smtp" != "xno" && test
 		CPPFLAGS="$CPPFLAGS_SAVE"
 		LDFLAGS="$LDFLAGS_SAVE"
 	else
-		PKG_CHECK_MODULES(libesmtp, libesmtp-1.0)
+		PKG_CHECK_MODULES(LIBESMTP, libesmtp-1.0, libesmtp="yes", libesmtp="no")
+		if test "x$libesmtp" = "xno"; then
+			AC_MSG_CHECKING(for libESMTP with libesmtp-config)
+			if libesmtp-config --version >/dev/null 2>&1; then
+				AC_MSG_RESULT(yes)
+				LIBESMTP_CFLAGS="`libesmtp-config --cflags`"
+				LIBESMTP_LIBS="`libesmtp-config --libs`"
+				libesmtp="yes"
+			else
+				AC_MSG_RESULT(no)
+				libesmtp=no
+			fi
+                fi
 	fi
-	enable_smtp="yes"
+	if test "x$enable_smtp" = "xyes" && test "x$libesmtp" = "xno"; then
+		AC_MSG_ERROR(libESMTP not found)
+	fi
+	enable_smtp=$libesmtp
 fi
 
 dnl ***************************************************************************