title: Swift Mailer - send emails asynchronnously
body: <p>on a project with intensive emailing activity we are creating asynchronnous workflow for posting emails. Workflow consists of 2 steps:</p>
  
  <ol>
  <li><p>creating the message (we set Subject, From, to, body, attachments), then converting to a string via <code>$mailer-&gt;toString()</code> and store into database.</p></li>
  <li><p>get few latest emails from database and send them out to user(s).</p></li>
  </ol>
  
  <p>String stored into database is actually valid multipart EML file (e.g. can be open with Outlook) with message headers + body.</p>
  
  <p>QUESTION:</p>
  
  <p><strong>How can I send message converted toString via SwiftMailer using it's transport capabilities?</strong></p>
  
  <p>Thank you.</p>
  
  <p>Example of stored string in the database:</p>
  
  <pre><code>Message-ID: &lt;1803a1a74c7612e43d58a8ca558117f3@refactoring.local&gt;
  Date: Mon, 16 Oct 2017 13:50:31 +0200
  Subject: Sample subject
  From: info@refactoring.local
  Reply-To: info@refactoring.local
  To: aaa@bbb.cc
  MIME-Version: 1.0
  Content-Type: multipart/alternative;
   boundary="_=_swift_v4_1508154632_faf5d3b80866048d993d77a62a9e6497_=_"
  
  --_=_swift_v4_1508154632_faf5d3b80866048d993d77a62a9e6497_=_
  Content-Type: text/plain; charset=utf-8
  Content-Transfer-Encoding: quoted-printable
  
  sample body ...
  
  --_=_swift_v4_1508154632_faf5d3b80866048d993d77a62a9e6497_=_
  Content-Type: text/html; charset=utf-8
  Content-Transfer-Encoding: quoted-printable
  
  &lt;!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org=
  /TR/xhtml1/DTD/xhtml1-strict.dtd"&gt;
  &lt;html xmlns=3D"http://www.w3.org/1999/xhtml"&gt;
  &lt;head&gt;
  =09&lt;meta http-equiv=3D"Content-Type" content=3D"text/html; charset=3DUTF-8"=
   /&gt;
  =09&lt;title&gt;Sample title&lt;/title&gt;
  =09&lt;/head&gt;
  &lt;body&gt;
  =09=09
  
  =09sample body ...
  =09&lt;/body&gt;
  &lt;/html&gt;
  
  --_=_swift_v4_1508154632_faf5d3b80866048d993d77a62a9e6497_=_--
  </code></pre>