diff -urN src.orig/parse.c src/parse.c
--- src.orig/parse.c	2008-03-04 23:25:54.000000000 +0200
+++ src/parse.c	2008-03-04 23:28:43.000000000 +0200
@@ -876,6 +876,7 @@
 uschar *p, *t;
 int hlen;
 BOOL coded = FALSE;
+BOOL first_byte = FALSE;
 
 if (charset == NULL) charset = US"iso-8859-1";
 
@@ -893,7 +894,7 @@
   int ch = *s++;
   if (t > buffer + buffer_size - hlen - 8) break;
 
-  if (t - p > 70)
+  if ((t - p > 67) && !first_byte)
     {
     *t++ = '?';
     *t++ = '=';
@@ -907,14 +908,15 @@
   if (ch < 33 || ch > 126 ||
       Ustrchr("?=()<>@,;:\\\".[]_", ch) != NULL)
     {
-    if (ch == ' ') *t++ = '_'; else
+    if (ch == ' ') { *t++ = '_'; first_byte = FALSE; } else
       {
       sprintf(CS t, "=%02X", ch);
       while (*t != 0) t++;
       coded = TRUE;
+      first_byte = !first_byte;
       }
     }
-  else *t++ = ch;
+  else { *t++ = ch; first_byte = FALSE; }
   }
 
 *t++ = '?';