Bu şekilde kullanabilirsiniz;
$icerik = '<tbody>
  <tr>
    <td align="center" style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative">
      <table width="100%" cellpadding="0" cellspacing="0" role="presentation" style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;-premailer-cellpadding: 0;-premailer-cellspacing: 0;-premailer-width: 100%;margin: 0;padding: 0;width: 100%">
        <tbody>
          <tr>
            <td style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;padding: 25px 0;text-align: center">
              <a href="https://meetweb.me/" style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;color: #3d4852;font-size: 19px;font-weight: bold;text-decoration: none;display: inline-block" target="_blank" tabindex="-1" rel="external" class="external"><img style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;max-width: 100%;border: none" src="https://meetweb.me/features/assets/images/logo.svg"></a>
            </td>
          </tr>
          <tr>
            <td width="100%" cellpadding="0" cellspacing="0" style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;-premailer-cellpadding: 0;-premailer-cellspacing: 0;-premailer-width: 100%;background-color: #e8e6fa;border-bottom: 1px solid #e8e6fa;border-top: 1px solid #e8e6fa;margin: 0;padding: 0;width: 100%">
              <table align="center" width="570" cellpadding="0" cellspacing="0" role="presentation" style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;-premailer-cellpadding: 0;-premailer-cellspacing: 0;-premailer-width: 570px;background-color: #ffffff;border-color: #e8e5ef;border-radius: 2px;border-width: 1px;box-shadow: 0 2px 0 rgba(0, 0, 150, 0.025), 2px 4px 0 rgba(0, 0, 150, 0.015);margin: 0 auto;padding: 0;width: 570px">
                 
                <tbody>
                  <tr>
                    <td style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;max-width: 100vw;padding: 32px">
                      <h1 style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;color: #3d4852;font-size: 18px;font-weight: bold;margin-top: 0;text-align: left">Merhaba,</h1>
                      <p style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;font-size: 16px;line-height: 1.5em;margin-top: 0;text-align: left">Yapmış olduğunuz başvuru onaylanmıştır.</p>
                      <p style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;font-size: 16px;line-height: 1.5em;margin-top: 0;text-align: left">Sistem üzerinden mağazanızı oluşturmadan önce aşağıdaki butona tıklayarak üyeliğinizi oluşturabilirsiniz.</p>
                      <br />
                      <p style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;font-size: 16px;line-height: 1.5em;margin-top: 0;text-align: left">Sevgilerle,<br>
                      MeetWeb Müşteri Hizmetleri</p>
                    </td>
                  </tr>
                </tbody>
              </table>
            </td>
          </tr>
          <tr>
            <td style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative">
              <table align="center" width="570" cellpadding="0" cellspacing="0" role="presentation" style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;-premailer-cellpadding: 0;-premailer-cellspacing: 0;-premailer-width: 570px;margin: 0 auto;padding: 0;text-align: center;width: 570px">
                <tbody>
                  <tr>
                    <td align="center" style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;max-width: 100vw;padding: 32px">
                      <p style="box-sizing: border-box;font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";position: relative;line-height: 1.5em;margin-top: 0;color: #b0adc5;font-size: 12px;text-align: center">© 2021 MeetWeb. Tüm hakları saklıdır.</p>
                    </td>
                  </tr>
                </tbody>
              </table>
            </td>
          </tr>
        </tbody>
      </table>
    </td>
  </tr>
</tbody>
';