For better user experience it would be great to send both variants of an outgoing message
For example, it can be looking like
--00000000000064ba9505a6a13030
Content-Type: text/plain; charset="UTF-8"
Hello message simple
--00000000000064ba9505a6a13030
Content-Type: text/html; charset="UTF-8"
<div dir="auto">Hello message simple</div>
--00000000000064ba9505a6a13030--

The current version looks like
------sinikael-?=_1-15905862099200.9206334027998657
Content-Type: text/plain
Content-Transfer-Encoding: quoted-printable
Test simple message
------sinikael-?=_1-15905862099200.9206334027998657--
