Wrong Content-Disposition encoding for '.'?

Sending an attachment with a filename containing an german umlaut e.g. 'tüst.pdf' results in a wrong 'Content-Disposition' encoding as the dot sign ('.') is escaped (at least some android mail apps seem to have problem with this, not decoding the escaped dot, resulting in a wrong filename extension):

--QUQ6IlsLsVLQY6lL
Content-Type: application/pdf
Content-Disposition: attachment; filename*=iso-8859-1''t%FCst%2Epdf
Content-Transfer-Encoding: base64

A quick fix is the following patch:

diff --git a/sendlib.c b/sendlib.c
index 204b1308..9f2e3e06 100644
--- a/sendlib.c
+++ b/sendlib.c
@@ -74,7 +74,7 @@ extern char **environ;
 
 extern char RFC822Specials[];
 
-const char MimeSpecials[] = "@.,;:<>[]\\\"()?/= \t";
+const char MimeSpecials[] = "@,;:<>[]\\\"()?/= \t";
 
 const char B64Chars[64] = {
   'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O',

Did try to search and read the appropriate RFC's and/or examples (e.g. [1]), seems all do NO escaping of the filename extension dot...

[1] http://test.greenbytes.de/tech/tc2231/#encoding-2231-char