$config['sys']['mail']['encoding']         = 'quoted-printable';     // Какое кодирование использовать в письмах: 8bit, 7bit, binary, base64, quoted-printable

$config['sys']['mail']['encoding']         = 'quoted-printable';

The values «8bit», «7bit», and «binary» all imply that NO encoding has been performed. However, they are potentially useful as indications of the kind of data contained in the object, and therefore of the kind of encoding that might need to be performed for transmission in a given transport system. «7bit» means that the data is all represented as short lines of US-ASCII data. «8bit» means that the lines are short, but there may be non-ASCII characters (octets with the high-order bit set). «Binary» means that not only may non-ASCII characters be present, but also that the lines are not necessarily short enough for SMTP transport.

The difference between «8bit» (or any other conceivable bit-width token) and the «binary» token is that «binary» does not require adherence to any limits on line length or to the SMTP CRLF semantics, while the bit-width tokens do require such adherence. If the body contains data in any bit-width other than 7-bit, the appropriate bit-width Content-Transfer-Encoding token must be used (e.g., «8bit» for unencoded 8 bit wide data). If the body contains binary data, the «binary» Content-Transfer-Encoding token must be used.

The Quoted-Printable encoding is intended to represent data that largely consists of octets that correspond to printable characters in the ASCII character set. It encodes the data in such a way that the resulting octets are unlikely to be modified by mail transport. If the data being encoded are mostly ASCII text, the encoded form of the data remains largely recognizable by humans. A body which is entirely ASCII may also be encoded in Quoted-Printable to ensure the integrity of the data should the message pass through a character-translating, and/or line-wrapping gateway.

Binary encoding is simply unencoded binary data. It has no line-length limitations. Binary encoded messages are not valid Internet messages.

$config['sys']['mail']['encoding']  = 'quoted-printable';

Короче binary — не правильно.

… или 64bit.

$config['sys']['mail']['charset']          = 'UTF-8';

Нет, ну я всё понимаю..., а как быть — если мои пользователи при этих изменениях получают письма с сайта нормального вида с рабочими ссылками?

To: user1 <user1@user.com>
Subject: =?UTF-8?B?0KDQtdCz0LjRgdGC0YDQsNGG0LjRjw==?=
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Date: Wed, 24 Sep 2014 18:03:06 +0400
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From: =?UTF-8?B?0JTQvdC10LLQvdC40LrQuCBhcnRkYXkuY2x1Yg==?= <admin@admin.adm>
Message-ID: <c7609c6c0eb21eb1ec26d9fef957df67@localhost>
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MIME-Version: 1.0
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

=D0=92=D1=8B =D0=B7=D0=B0=D1=80=D0=B5=D0=B3=D0=B8=D1=81=D1=82=D1=80=D0=
=B8=D1=80=D0=BE=D0=B2=D0=B0=D0=BB=D0=B8=D1=81=D1=8C =D0=BD=D0=B0 =D1=81=
=D0=B0=D0=B9=D1=82=D0=B5 <a href=3D"http://localhost/">=D0=94=D0=BD=D0=
=B5=D0=B2=D0=BD=D0=B8=D0=BA=D0=B8 example.com</a>
=D0=92=D0=B0=D1=88=D0=B8 =D1=80=D0=B5=D0=B3=D0=B8=D1=81=D1=82=D1=80=D0=
=B0=D1=86=D0=B8=D0=BE=D0=BD=D0=BD=D1=8B=D0=B5 =D0=B4=D0=B0=D0=BD=D0=BD=
=D1=8B=D0=B5:
   =D0=BB=D0=BE=D0=B3=D0=B8=D0=BD: <b>user1</b>
   =D0=BF=D0=B0=D1=80=D0=BE=D0=BB=D1=8C: <b>user1</b>


=D0=A1 =D1=83=D0=B2=D0=B0=D0=B6=D0=B5=D0=BD=D0=B8=D0=B5=D0=BC, =D0=B0=D0=
=B4=D0=BC=D0=B8=D0=BD=D0=B8=D1=81=D1=82=D1=80=D0=B0=D1=86=D0=B8=D1=8F =
=D1=81=D0=B0=D0=B9=D1=82=D0=B0 <a href=3D"http://localhost/">=D0=94=D0=
=BD=D0=B5=D0=B2=D0=BD=D0=B8=D0=BA=D0=B8 example.com</a>

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