diff -r 2b3fb2398f45 Lib/email/charset.py
--- a/Lib/email/charset.py	Wed Mar 16 22:11:09 2011 -0400
+++ b/Lib/email/charset.py	Thu Mar 17 12:20:01 2011 -0400
@@ -390,7 +390,9 @@
         if self.body_encoding is BASE64:
             if isinstance(string, str):
                 string = string.encode(self.output_charset)
-            return email.base64mime.body_encode(string)
+            cteinput = b'\r\n'.join(string.splitlines()) + (
+                            b'\r\n' if string[-1] in b'\r\n' else b'')
+            return email.base64mime.body_encode(cteinput)
         elif self.body_encoding is QP:
             return email.quoprimime.body_encode(string)
         else: