I am using a conditional statement for all versions of Outlook desktop/web email. I'm not sure if this link helps: https://www.htmlemailcheck.com/knowledge-base/recommended-externalclass-css-fix-outlook-com/

But, in mobile I am using a media query to show the ad in the content (so see ad higher up in the email) but also hide the same ad in the right rail when it wraps below the content.

The email has passed testing in the following:
iOS Third Party apps: Yahoo, Gmail, Outlook, iOS email -- content ad displays/right rail ad does not
Android 5 email -- content ad displays/right rail ad does not
Desktop: Mac OS X Outlook app (15.40) -- content ad does not display/right rail does

and PC Windows 7 Outlook Office 365 -- content ad does not display/right rail does
Web email Mac (FF 57) and PC (Chrome 62, IE 11) Yahoo, Gmail, AOL -- content ad does not display/right rail does

Here is the html:


                    <!--[if (gte mso 9)|(IE)]>
                    <div style="display:none;width:0px;height:0px;overflow:hidden;opacity: 0;mso-hide:all;">
                    <![endif]-->
                    <table width="100%" cellpadding="0" cellspacing="0" border="0" style="border-spacing: 0;">
                      <tr>
                        <td align="center">
                          <!-- MedRectangle Advertising -->
                          <table class="open-mobile" width="100%" cellpadding="0" cellspacing="0" border="0" style="border-top-width: 1px; border-top-style: solid; border-top-color: #1a1a1a; mso-hide:all;">
                            <tr>
                              <td align="center" style="padding-top: 20px; padding-bottom: 4px; color: #999999;font-family: Helvetica, Arial, sans-serif; font-size: 9px; letter-spacing: 0.12em; line-height: 11px;">ADVERTISEMENT</td>
                            </tr>
                            <tr>
                              <td align="center" style="padding-bottom: 32px;"><a href="http://www.adtechus.com"><img src="http://pchan.nejm.org/NEJM-Refresh/eTOC-0717/alt-mobile_1117/pharma.png" alt="Advertisement" width="300" height="250" style="border-width: 0;" /></a></td>
                            </tr>
                          </table>
                        </td>
                      </tr>
                    </table>
                  <!--[if (gte mso 9)|(IE)]>
                  </div>
                  <![endif]-->

And here is the media query:


    @media screen and (min-width: 728px) {
      .webkit {
        width: 728px !important;
      }

      .right-sidebar .left {
        max-width: 403px;
      }

      .right-sidebar .right {
        max-width: 320px;
      }
      .open-mobile {
        display: none;
      }
    }
    @media screen and (max-width: 728px) {
      .hide-desktop {
        display: none;
      }
      .open-mobile {
        display: inline-block !important;
        width: 100% !important;
        height: 100% !important;
        overflow: visible !important;
        opacity: 100 !important;
      }
    }

And finally a link to a screen capture taken from my test Office 365 email: http://images.nejm.org/email/office-365.png
Appreciate your help.