Hello, I tried to send mail with polish characters "śćńółęśąśżćźó",
also I added correct headers "Content-type: text/html; charset=UTF-8" and file encoding
but in sendmail output logs and on gmail, the message looks like:
"L>A?L"AlL,ATL>A.L>LLA?LsAl".

Sendmail output logs:

17.03.31 16:02:58 ** --- MESSAGE BEGIN --- 17.03.31 16:02:58 ** To: ***@gmail.com 17.03.31 16:02:58 ** Subject: test 17.03.31 16:02:58 ** X-PHP-Originating-Script: 0:index.php 17.03.31 16:02:58 ** Content-type: text/html; charset=UTF-8 17.03.31 16:02:58 ** 17.03.31 16:02:58 ** śćńółęśąśżćźó 17.03.31 16:02:58 ** --- MESSAGE END --- 17.03.31 16:02:59 >> Date: Fri, 31 Mar 2017 16:02:59 <EOL> 17.03.31 16:02:59 >> To: ***@gmail.com<EOL> 17.03.31 16:02:59 >> Subject: test<EOL> 17.03.31 16:02:59 >> X-PHP-Originating-Script: 0:index.php<EOL> 17.03.31 16:02:59 >> Content-type: text/html; charset=UTF-8<EOL> 17.03.31 16:02:59 >> <EOL> 17.03.31 16:02:59 >> L>A?L"AlL,ATL>A.L>LLA?LsAl<EOL> 17.03.31 16:02:59 >> .<EOL>

Any ideas?