Web Addin - OnMessageSend - Soft Blocking/Prompt User is not working in Outlook Classic

[aberamdatazoic]

Issue Description:
I am creating a web add-in that hooks to the send email button. When the user clicks send, it is supposed to first pull the to, subject and content and send it to my API, before allowing the email to send. It works as expected when used on OWA and the New Outlook Desktop but it does not work on the Classic Outlook. The function which we declared in our JS function is not being called. The User Prompt is only supposed to show if the Addin is not available. In this case even if the web add-in has loaded (as seen in the screenshot), it is not triggering our JS function.

Screenshot:

Below are our codes which can reproduce this issue.

Manifest File:

<?xml version="1.0" encoding="UTF-8"?>
<OfficeApp xmlns="http://schemas.microsoft.com/office/appforoffice/1.1" 
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
           xmlns:bt="http://schemas.microsoft.com/office/officeappbasictypes/1.0" 
           xmlns:mailappor="http://schemas.microsoft.com/office/mailappversionoverrides" 
           xsi:type="MailApp">
  <Id>d9d81f5a-e002-4475-88bc-cc51e3c97816</Id>
  <Version>1.0.0</Version>
  <ProviderName>DZ</ProviderName>
  <DefaultLocale>en-US</DefaultLocale>
  <DisplayName DefaultValue="DZ" />
  <Description DefaultValue="DZ"/>
  <IconUrl DefaultValue="https://emt.datazoic.com/prismimg/Icon96.png"/>
  <HighResolutionIconUrl DefaultValue="https://emt.datazoic.com/prismimg/Icon96.png" />
  <Hosts>
    <Host Name="Mailbox" />
  </Hosts>
  <Requirements>
    <Sets>
      <Set Name="Mailbox" MinVersion="1.3" />
    </Sets>
  </Requirements>
  <FormSettings>
    <Form xsi:type="ItemRead">
      <DesktopSettings>
		  <SourceLocation DefaultValue="https://prismdev.datazoic.com/prismST/webaddin/launchEvnt.html" />
        <RequestedHeight>250</RequestedHeight>
      </DesktopSettings>
    </Form>
  </FormSettings>
  <Permissions>ReadWriteItem</Permissions>
  <Rule xsi:type="RuleCollection" Mode="Or">
    <Rule xsi:type="ItemIs" ItemType="Message" FormType="Read"/>
  </Rule>
  <DisableEntityHighlighting>true</DisableEntityHighlighting>
 <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides" xsi:type="VersionOverridesV1_0">
    <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides/1.1" xsi:type="VersionOverridesV1_1">
      <Requirements>
        <bt:Sets DefaultMinVersion="1.12">
          <bt:Set Name="Mailbox" />
        </bt:Sets>
      </Requirements>
      <Hosts>
        <Host xsi:type="MailHost">
          <Runtimes>
            <Runtime resid="functionFile" >
               <Override type="javascript" resid="JSRuntime.Url"/>
            </Runtime>
          </Runtimes>
          <DesktopFormFactor>
            <FunctionFile resid="functionFile" />
            <ExtensionPoint xsi:type="LaunchEvent">
				<LaunchEvents>
					<LaunchEvent Type="OnMessageSend" FunctionName="onSendBtnClick" SendMode="PromptUser" />
				</LaunchEvents>
				<SourceLocation resid="functionFile"/>
			</ExtensionPoint>
			<ExtensionPoint xsi:type="MessageComposeCommandSurface">
            <OfficeTab id="TabDefault">
              <Group id="translateGroup">
                <Label resid="groupLabel" />
                <Control xsi:type="Button" id="msgSmartSend">
                  <Label resid="paneSmartSendButtonLabel" />
                  <Supertip>
                    <Title resid="paneSmartSendSuperTipTitle" />
                    <Description resid="paneSmartSendSuperTipDescription" />
                  </Supertip>
                  <Icon>
                    <bt:Image size="16" resid="smartsent96" />
                    <bt:Image size="32" resid="smartsent96" />
                    <bt:Image size="80" resid="smartsent96" />
                  </Icon>
                  <Action xsi:type="ShowTaskpane">
                    <SourceLocation resid="messageReadTaskPaneSmartSendUrl" />
                    <SupportsPinning>true</SupportsPinning>
                  </Action>
                </Control>
			  </Group>
            </OfficeTab>
          </ExtensionPoint>
          </DesktopFormFactor>
        </Host>
      </Hosts>
      <Resources>
		  <bt:Images>
			<bt:Image id="smartsent96" DefaultValue="https://emt.datazoic.com/prismimg/smartsent96.png"/>
		  </bt:Images>
          <bt:Urls>
           <bt:Url id="functionFile" DefaultValue="https://prismdev.datazoic.com/prismST/webaddin/launchEvnt.html" />
           <bt:Url id="JSRuntime.Url" DefaultValue="https://prismdev.datazoic.com/prismST/webaddin/launchEvnt.js" />
		   <bt:Url id="messageReadTaskPaneSmartSendUrl" DefaultValue="https://prismdev.datazoic.com/prismST/webaddin/launchEvnt.html"/>
          </bt:Urls>
		  <bt:ShortStrings>
			<bt:String id="groupLabel" DefaultValue="DZ"/>
			<bt:String id="customTabLabel"  DefaultValue="DZ Tab"/>
			<bt:String id="paneSmartSendButtonLabel" DefaultValue="Smart Send"/>
			<bt:String id="paneSmartSendSuperTipTitle" DefaultValue="Smart Send"/>
		  </bt:ShortStrings>
		  <bt:LongStrings>
			<bt:String id="paneReadSuperTipDescription" DefaultValue="Opens a pane displaying all available properties. This is an example of a button that opens a task pane."/>
			<bt:String id="paneSmartSendSuperTipDescription" DefaultValue="Smart Send."/>
		  </bt:LongStrings>
      </Resources>
    </VersionOverrides>  
  </VersionOverrides>
</OfficeApp>

Launch Event HTML Code:

<!DOCTYPE html>
<html class="newhtml">
	<head>
		<title>DZ</title>
		<meta name="robots" content="noindex">
		<meta charset="utf-8"/>
		<meta http-equiv='X-UA-Compatible' content="IE=edge" />
		<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
		<meta http-equiv="cache-control" content="max-age=0" />
		<meta http-equiv="cache-control" content="no-cache, must-revalidate, post-check=0, pre-check=0" />
		<meta name="viewport" content="width=device-width, initial-scale=1.0" />
		<meta http-equiv="Pragma" content="no-cache" />
		<meta http-equiv="Expires" content="-1" />
	</head>
	
	<body class="" data-scroll-top="false">
		<div>DZ Panel</div>
		<script src="https://appsforoffice.microsoft.com/lib/1/hosted/office.js" type="text/javascript"></script> 
		<script type="text/javascript" src="launchEvnt.js"></script>
	</body>
</html>

Launch Event JS Code:

Office.initialize = function(reason){
	Office.onReady(function(info){
		console.log('Office is ready to use');
	});
}
try{
	Office.actions.associate("onMessageSendHandler", onSendBtnClick);
}catch(e){
	console.log(e);
}
async function onSendBtnClick(event){
	try{
		console.log(event);
		event.completed({ allowEvent: true });
	}catch(e){
		console.log(e);
	}
}

Environment:

• Platform: Classic Outlook
• Office version number: Microsoft® Outlook® for Microsoft 365 MSO (Version 2411 Build 16.0.18227.20082) 64-bit
• Operating System: Windows 10 Pro