title: MailKit smtp.office365.com special character encoding issue
body: <p>First, I do not know if my issue come from a bad use of Mailkit (that is a great piece of software, by the way) or a miss-configuration of smtp.office365.com.</p>
  
  <p>Version of MailKit is: 2.6.0</p>
  
  <p>I try to send a message with this string <code>Test d'ênvoïe d'èmail avec des àccénts</code>, in the subject and text body. </p>
  
  <p>When I use the smtp.office365.com account to send the email, when I received it in my office 365 box, the subject is fine, but the body look like this <code>Test d'�nvo�e d'�mail avec des �cc�nts</code>.</p>
  
  <p>I try to use another smtp.office365.com account from another company, and when I received it in my office 365 box, the subject and the body are fine.</p>
  
  <p>I try to send the same email with the first smtp account to a GMAIL email box. The subject and the body were fine.</p>
  
  <p>So I don’t know if the first smtp account is miss-configured, or outlook (desktop and web) are buggy ?</p>
  
  <p>The code that sends the email is quite simple and nothing fancy is used. This code is used every day to send emails from our software, and this is the first time we have this kind of problem with a smtp. What bothers me is that it’s an office 365 smtp, like the one we use every day without any trouble.</p>
  
  <p>--- EDIT
  As requested by @jstedfast here is the raw MIME generated by MimeKit/MailKit</p>
  
  <pre><code>From: email@domain.com
  Date: Tue, 26 May 2020 14:16:13 +0000
  Subject: Test =?utf-8?b?ZCfDqm52b8OvZSBkJ8OobWFpbCBhdmVjIGRlcyDDoGNjw6ludHM=?=
  Message-Id: &lt;54G3D036QAU4.3G654QDV2MVS2@4b245b0f83f4&gt;
  To: some@email.com
  MIME-Version: 1.0
  Content-Type: multipart/alternative; boundary="=-xjuWE0kh6/lmMc7JIcMJ3g=="
  
  --=-xjuWE0kh6/lmMc7JIcMJ3g==
  Content-Type: text/plain; charset=utf-8
  
  Test d'ênvoïe d'èmail avec des àccénts ça, ~ $ #{][*µµ$£= +
  --=-xjuWE0kh6/lmMc7JIcMJ3g==
  Content-Type: text/html; charset=utf-8
  Content-Id: &lt;RUL3D036QAU4.Y7K3UPECLV0Q3@4b245b0f83f4&gt;
  
  Test d'ênvoïe d'èmail avec des àccénts ça, ~ $ #{][*µµ$£= +
  --=-xjuWE0kh6/lmMc7JIcMJ3g==--
  </code></pre>