By default, a part will be encoded as quoted-printable when it contains any non-ASCII characters (characters with the 8th bitset), or if there are any lines longer than MAXLEN characters(default value 200). 標準では、非 ASCII 文字 (8 ビット目がセットされている文字) を含むか、MAXLEN 文字 (標準の値は 200 です) よりも長い部分は quoted-printable 形式で符号化されます。 - Python
Copyright 2001-2004 Python Software Foundation.All rights reserved. Copyright 2000 BeOpen.com.All rights reserved. Copyright 1995-2000 Corporation for National Research Initiatives.All rights reserved. Copyright 1991-1995 Stichting Mathematisch Centrum.All rights reserved.