Sending HTML message with wrong letters format

Hi everyone,

I came across an issue with polish letters in message.
I copied the HTML formatted message from Outlook2013 to mail body and added the utf-8 format:

<META HTTP-EQUIV=‘Content-Type’ CONTENT=‘text/html; charset=utf-8’>

Although it should work fine, I still receive message with strange sings, not the correct ones.
Any help would be appreciated.