Show Outlook Add-in without compose or read pane active

Question

Hello I am testing an outlook Add-in in visual studio, but I do not know that to change in the manifest to show the add-in enable all the time, without opening an email or read an email.

Currently is only enable or showing when an email is open, the rest of the time is disable And I want to be enable all the time

<?xml version="1.0" encoding="UTF-8"?>
<!--Created:ce44715c-8c4e-446b-879c-ea9ebe0f09c8-->
<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/1.0" 
          xsi:type="MailApp">

  <!-- Begin Basic Settings: Add-in metadata, used for all versions of Office unless override provided. -->

  <!-- IMPORTANT! Id must be unique for your add-in, if you reuse this manifest ensure that you change this id to a new GUID. -->
  <Id>65ba8340-b53e-4941-a7bb-153669eea7fb</Id>

  <!--Version. Updates from the store only get triggered if there is a version change. -->
  <Version>1.0.0.0</Version>
  <ProviderName>[Provider name]</ProviderName>
  <DefaultLocale>en-US</DefaultLocale>
  <!-- The display name of your add-in. Used on the store and various places of the Office UI such as the add-ins dialog. -->
  <DisplayName DefaultValue="OutlookWebAddIn1" />
  <Description DefaultValue="OutlookWebAddIn1"/>
  <IconUrl DefaultValue="~remoteAppUrl/Images/icon64.png"/>

  <SupportUrl DefaultValue="http://www.contoso.com" />
  <!-- Domains that will be allowed when navigating. For example, if you use ShowTaskpane and then have an href link, navigation will only be allowed if the domain is on this list. -->
  <AppDomains>
    <AppDomain>AppDomain1</AppDomain>
    <AppDomain>AppDomain2</AppDomain>
    <AppDomain>AppDomain3</AppDomain>
  </AppDomains>
  <!--End Basic Settings. -->
  
  <Hosts>
    <Host Name="Mailbox" />
  </Hosts>
  <Requirements>
    <Sets>
      <Set Name="Mailbox" MinVersion="1.1" />
    </Sets>
  </Requirements>
  <FormSettings>
    <Form xsi:type="ItemRead">
      <DesktopSettings>
        <SourceLocation DefaultValue="~remoteAppUrl/MessageRead.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>false</DisableEntityHighlighting>

  <VersionOverrides xmlns="http://schemas.microsoft.com/office/mailappversionoverrides" xsi:type="VersionOverridesV1_0">
    <Requirements>
      <bt:Sets DefaultMinVersion="1.3">
        <bt:Set Name="Mailbox" />
      </bt:Sets>
    </Requirements>
    <Hosts>
      <Host xsi:type="MailHost">

        <DesktopFormFactor>
          <!-- Location of the Functions that UI-less buttons can trigger (ExecuteFunction Actions). -->
          <FunctionFile resid="functionFile" />

          <!-- Message Read -->
          <ExtensionPoint xsi:type="MessageReadCommandSurface">
            <!-- Use the default tab of the ExtensionPoint or create your own with <CustomTab id="myTab"> -->
            <OfficeTab id="TabDefault">
              <!-- Up to 6 Groups added per Tab -->
              <Group id="msgReadGroup">
                <Label resid="groupLabel" />
                <!-- Launch the add-in : task pane button -->
                <Control xsi:type="Button" id="msgReadOpenPaneButton">
                  <Label resid="paneReadButtonLabel" />
                  <Supertip>
                    <Title resid="paneReadSuperTipTitle" />
                    <Description resid="paneReadSuperTipDescription" />
                  </Supertip>
                  <Icon>
                    <bt:Image size="16" resid="icon16" />
                    <bt:Image size="32" resid="icon32" />
                    <bt:Image size="80" resid="icon80" />
                  </Icon>
                  <Action xsi:type="ShowTaskpane">
                    <SourceLocation resid="messageReadTaskPaneUrl" />
                  </Action>
                </Control>
                <!-- Go to http://aka.ms/ButtonCommands to learn how to add more Controls: ExecuteFunction and Menu -->
              </Group>
            </OfficeTab>
          </ExtensionPoint>
          <!-- Go to http://aka.ms/ExtensionPointsCommands to learn how to add more Extension Points: MessageRead, AppointmentOrganizer, AppointmentAttendee -->
        </DesktopFormFactor>
      </Host>
    </Hosts>

    <Resources>
      <bt:Images>
        <bt:Image id="icon16" DefaultValue="~remoteAppUrl/Images/icon16.png"/>
        <bt:Image id="icon32" DefaultValue="~remoteAppUrl/Images/icon32.png"/>
        <bt:Image id="icon80" DefaultValue="~remoteAppUrl/Images/icon80.png"/>
      </bt:Images>
      <bt:Urls>
        <bt:Url id="functionFile" DefaultValue="~remoteAppUrl/Functions/FunctionFile.html"/>
        <bt:Url id="messageReadTaskPaneUrl" DefaultValue="~remoteAppUrl/MessageRead.html"/>
      </bt:Urls>
      <bt:ShortStrings>
        <bt:String id="groupLabel" DefaultValue="My Add-in Group"/>
        <bt:String id="customTabLabel"  DefaultValue="My Add-in Tab"/>
        <bt:String id="paneReadButtonLabel" DefaultValue="Display all properties"/>
        <bt:String id="paneReadSuperTipTitle" DefaultValue="Get all properties"/>
      </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:LongStrings>
    </Resources>
  </VersionOverrides>
</OfficeApp>

Answer 1

Outlook web add-ins work under the context of a particular item - composed or read. You can't run the add-in for the mailbox by default. It is not possible at least now. I'd suggest posting a feature request to Microsoft 365 Developer Platform Tech Community.

As a workaround, you may consider developing a COM based add-in where you can enable ribbon buttons independently of the selected item(s). See Walkthrough: Create your first VSTO Add-in for Outlook for more information.