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Troubleshoot Outlook contextual add-in activation

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Outlook contextual add-in activation is based on the activation rules in an add-in only manifest for the add-in. When conditions for the currently selected item satisfy the activation rules for the add-in, the application activates and displays the add-in button in the Outlook UI (add-in selection pane for compose add-ins, add-in bar for read add-ins). However, if your add-in doesn't activate as you expect, you should look into the following areas for possible reasons.

Important

Entity-based contextual Outlook add-ins are now retired. As an alternative solution, implement regular expression rules in your contextual add-in. For guidance on how to implement these rules, see Contextual Outlook add-ins.

Is user mailbox on a version of Exchange Server that is at least Exchange 2016?

First, ensure that the user's email account you're testing with is on a version of Exchange Server that is at least Exchange 2016. If you're using specific features that are released after Exchange 2016, make sure the user's account is on the appropriate version of Exchange.

You can verify the version of Exchange by using one of the following approaches.

  • Check with your Exchange Server administrator.

  • If you're testing the add-in on Outlook on the web or mobile devices, in a script debugger (for example, the JScript Debugger that comes with Internet Explorer), look for the src attribute of the script tag that specifies the location from which scripts are loaded. The path should contain a substring owa/15.0.516.x/owa2/..., where 15.0.516.x represents the version of the Exchange Server, such as 15.0.516.2.

  • Alternatively, you can use the Office.context.mailbox.diagnostics.hostVersion property to verify the version. In Outlook on the web, on mobile devices, and in new Outlook on Windows, this property returns the version of the Exchange Server.

  • If you can test the add-in on Outlook, you can use the following simple debugging technique that uses the Outlook object model and Visual Basic Editor.

    1. First, verify that macros are enabled for Outlook. Choose File, Options, Trust Center, Trust Center Settings, Macro Settings. Ensure that Notifications for all macros is selected in the Trust Center. You should have also selected Enable Macros during Outlook startup.

    2. On the Developer tab of the ribbon, choose Visual Basic.

      Note

      Not seeing the Developer tab? See How to: Show the Developer Tab on the Ribbon to turn it on.

    3. In the Visual Basic Editor, choose View, Immediate Window.

    4. Type the following in the Immediate window to display the version of the Exchange Server. The major version of the returned value must be equal to or greater than 15.

      • If there is only one Exchange account in the user's profile:
       ?Session.ExchangeMailboxServerVersion
      • If there are multiple Exchange accounts in the same user profile (emailAddress represents a string that contains the user's primary SMTP address):
       ?Session.Accounts.Item(emailAddress).ExchangeMailboxServerVersion

Is the add-in available?

Outlook on Windows (classic) and on Mac can make an add-in unavailable due to performance reasons, including exceeding usage thresholds for CPU core or memory, tolerance for crashes, and length of time to process all the regular expressions for an add-in. When this happens, Outlook on Windows (classic) and on Mac display a notification that it's making an add-in unavailable.

Note

Only Outlook on Windows (classic) and Outlook on Mac monitor resource usage. However, an add-in made unavailable in Outlook on Windows (classic) or Outlook on Mac also becomes unavailable in Outlook on the web, on mobile devices, and in new Outlook on Windows.

Check your list of installed add-ins to verify whether an add-in is available. For instructions on how to view your add-ins in Outlook, see Use add-ins in Outlook.

Does the tested item support Outlook add-ins? Is the selected item delivered by a version of Exchange Server that is at least Exchange 2016?

If your Outlook add-in is a read add-in and is supposed to be activated when the user is viewing a message (including email messages, meeting requests, responses, and cancellations) or appointment, even though these items generally support add-ins, there are exceptions. Check if the selected item is one of those listed where Outlook add-ins don't activate.

Also, because appointments are always saved in Rich Text Format, an ItemHasRegularExpressionMatch rule that specifies a PropertyName value of BodyAsHTML wouldn't activate an add-in on an appointment or message that's saved in plain text or Rich Text Format.

Is the add-in manifest installed properly, and does Outlook have a cached copy?

Note

Outlook add-in features that depend on activation rules aren't supported when the add-in uses a unified app manifest for Microsoft 365.

This scenario applies to only classic Outlook on Windows. Normally, when you install an Outlook add-in for a mailbox, the Exchange Server copies the add-in manifest from the location you indicate to the mailbox on that Exchange Server. Every time Outlook starts, it reads all the manifests installed for that mailbox into a temporary cache at the following location.

%LocalAppData%\Microsoft\Office\16.0\WEF

For example, for the user John, the cache might be at C:\Users\john\AppData\Local\Microsoft\Office\16.0\WEF.

If an add-in doesn't activate for any items, the manifest might not have been installed properly on the Exchange Server, or Outlook hasn't read the manifest properly on startup. Using the Exchange Admin Center, ensure that the add-in is installed and enabled for your mailbox, and reboot the Exchange Server, if necessary.

The following figure shows a summary of the steps to verify whether Outlook has a valid version of the manifest.

Flow chart to check manifest.

The following procedure describes the details.

  1. If you have modified the manifest while Outlook is open, and you're not using Visual Studio 2015 or a later version of Visual Studio to develop the add-in, you should uninstall the add-in and reinstall it using the Exchange Admin Center.

  2. Restart Outlook and test whether Outlook now activates the add-in.

  3. If Outlook doesn't activate the add-in, check whether Outlook has a properly cached copy of the manifest for the add-in. Look under the following path.

    %LocalAppData%\Microsoft\Office\16.0\WEF

    You can find the manifest in the following subfolder.

    \<insert your guid>\<insert base 64 hash>\Manifests\<ManifestID>_<ManifestVersion>

    Note

    The following is an example of a path to a manifest installed for a mailbox for the user John.

    C:\Users\john\appdata\Local\Microsoft\Office\16.0\WEF\{8D8445A4-80E4-4D6B-B7AC-D4E6AF594E73}\GoRshCWa7vW8+jhKmyiDhA==\Manifests\b3d7d9d5-6f57-437d-9830-94e2aaccef16_1.2

    Verify whether the manifest of the add-in you're testing is among the cached manifests.

  4. If the manifest is in the cache, skip the rest of this section and consider the other possible reasons following this section.

  5. If the manifest is not in the cache, check whether Outlook indeed successfully read the manifest from the Exchange Server. To do that, use the Windows Event Viewer:

    1. Under Windows Logs, choose Application.

    2. Look for a reasonably recent event for which the Event ID equals 63, which represents Outlook downloading a manifest from an Exchange Server.

    3. If Outlook successfully read a manifest, the logged event should have the following description.

      The Exchange web service request GetAppManifests succeeded.

      Then skip the rest of this section and consider the other possible reasons following this section.

  6. If you don't see a successful event, close Outlook, and delete all the manifests in the following path.

    %LocalAppData%\Microsoft\Office\16.0\WEF\<insert your guid>\<insert base 64 hash>\Manifests\

    Start Outlook and test whether Outlook now activates the add-in.

  7. If Outlook doesn't activate the add-in, go back to Step 3 to verify again whether Outlook has properly read the manifest.

Is the add-in manifest valid?

See Validate and troubleshoot issues with your manifest to debug add-in manifest issues.

Are you using the appropriate activation rules?

Starting in version 1.1 of the Office Add-ins manifests schema, you can create add-ins that are activated when the user is in a compose form (compose add-ins) or in a read form (read add-ins). Make sure you specify the appropriate activation rules for each type of form that your add-in is supposed to activate in. For example, you can activate compose add-ins using only ItemIs rules with the FormType attribute set to Edit or ReadOrEdit, and you can't use any of the other types of rules, such as ItemHasRegularExpressionMatch rules for compose add-ins.

If you use a regular expression, is it properly specified?

Because regular expressions in activation rules are part of the XML-formatted add-in only manifest file for a read add-in, if a regular expression uses certain characters, be sure to follow the corresponding escape sequence that XML processors support. The following table lists these special characters.

Character Description Escape sequence to use
" Double quotation mark &quot;
& Ampersand &amp;
' Apostrophe &apos;
< Less-than sign &lt;
> Greater-than sign &gt;

If you use a regular expression, does the read add-in activate in Outlook on the web, on mobile devices, or in new Outlook on Windows, but not in Outlook on Windows (classic) or Outlook on Mac?

Outlook on Windows (classic) and Outlook on Mac use a regular expression engine that's different from the one used by Outlook on the web, on mobile devices, and on new Outlook on Windows. Classic Outlook on Windows and Outlook on Mac use the C++ regular expression engine provided as part of the Visual Studio standard template library. This engine complies with ECMAScript 5 standards. Outlook on the web, on mobile devices, and new Outlook on Windows use regular expression evaluation that's part of JavaScript, is provided by the browser, and supports a superset of ECMAScript 5.

While in most cases, these Outlook clients find the same matches for the same regular expression in an activation rule, there are exceptions. For instance, if the regex includes a custom character class based on predefined character classes, Outlook on Windows (classic) and Outlook on Mac may return results different from Outlook on the web, on mobile devices, and new Outlook on Windows. As an example, character classes that contain shorthand character classes [\d\w] within them would return different results. In this case, to avoid different results on different applications, use (\d|\w) instead.

Test your regular expression thoroughly. If it returns different results, rewrite the regular expression for compatibility with both engines. To verify evaluation results in Outlook on Windows (classic) and Outlook on Mac, write a small C++ program that applies the regular expression against a sample of the text you are trying to match. Running on Visual Studio, the C++ test program would use the standard template library, simulating the behavior of Outlook on Windows (classic) or Outlook on Mac when running the same regular expression. To verify evaluation results in Outlook on the web, on mobile devices, and in new Outlook on Windows, use your favorite JavaScript regular expression tester.

If you use an ItemHasRegularExpressionMatch activation rule, verify whether the value of the PropertyName attribute is what you expect for the selected item. The following are some tips to debug the corresponding properties.

  • If the selected item is a message and you specify BodyAsHTML in the PropertyName attribute, open the message, and then choose View Source to verify the message body in the HTML representation of that item.

  • If the selected item is an appointment, or if the activation rule specifies BodyAsPlaintext in the PropertyName, you can use the Outlook object model and the Visual Basic Editor in classic Outlook on Windows.

    1. Ensure that macros are enabled and the Developer tab is displayed on the ribbon for Outlook.

    2. In the Visual Basic Editor, choose View, Immediate Window.

    3. Type the following to display various properties depending on the scenario.

      • The HTML body of the message or appointment item selected in the Outlook explorer:
      ?ActiveExplorer.Selection.Item(1).HTMLBody
      • The plain text body of the message or appointment item selected in the Outlook explorer:
      ?ActiveExplorer.Selection.Item(1).Body
      • The HTML body of the message or appointment item opened in the current Outlook inspector:
      ?ActiveInspector.CurrentItem.HTMLBody
      • The plain text body of the message or appointment item opened in the current Outlook inspector:
      ?ActiveInspector.CurrentItem.Body

If the ItemHasRegularExpressionMatch activation rule specifies Subject or SenderSMTPAddress, or if you use an ItemIs or ItemHasAttachment rule, and you're familiar with or would like to use MAPI, use MFCMAPI. Verify the MAPI property that your rule relies on in the following table.

Type of rule Verify this MAPI property
ItemHasRegularExpressionMatch rule with Subject PidTagSubject
ItemHasRegularExpressionMatch rule with SenderSMTPAddress PidTagSenderSmtpAddress and PidTagSentRepresentingSmtpAddress
ItemIs PidTagMessageClass
ItemHasAttachment PidTagHasAttachments

After verifying the property value, you can then use a regular expression evaluation tool to test whether the regular expression finds a match in that value.

Does Outlook apply all the regular expressions to the portion of the item body as you expect?

This section applies to all activation rules that use regular expressions, particularly, those that are applied to the item body, which may be large in size and take longer to evaluate for matches. You should be aware that even if the item property that an activation rule depends on has the value you expect, Outlook may not be able to evaluate all the regular expressions on the entire value of the item property. To provide reasonable performance and to control excessive resource usage by a read add-in, Outlook observes the following limits on processing regular expressions in activation rules at runtime.

  • The size of the item body evaluated. There are limits to the portion of an item body on which Outlook evaluates a regular expression. These limits depend on the Outlook client, form factor, and format of the item body. For more information, see Limits on the size of the item body evaluated.

  • Number of regular expression matches. Outlook on the web, on Windows (new and classic), on Mac, and on mobile devices each returns a maximum of 50 regular expression matches. These matches are unique, and duplicate matches don't count against this limit. Don't assume any order to the returned matches, and don't assume the order in Outlook on Windows (classic) and Outlook on Mac is the same as that in Outlook on the web, on mobile devices, and in new Outlook on Windows. If you expect many matches to regular expressions in your activation rules, and you're missing a match, you may be exceeding this limit.

  • Length of a regular expression match. There are limits to the length of a regular expression match that the Outlook application would return. Outlook doesn't include any match above the limit and doesn't display any warning message. You can run your regular expression using other regex evaluation tools or a stand-alone C++ test program to verify whether you have a match that exceeds such limits. The following table summarizes the limits. For more information, see Limits of activation rules for contextual Outlook add-in.

    Limit on length of a regex match Outlook on the web, on new Windows client, and on mobile devices Outlook on Windows (classic) and on Mac
    Item body is plain text 3 KB 1.5 KB
    Item body is HTML 3 KB 3 KB

  • Time spent on evaluating all regular expressions of a read add-in in Outlook on Windows (classic) and Outlook on Mac. By default, for each read add-in, Outlook must finish evaluating all the regular expressions in its activation rules within one second. Otherwise, Outlook retries up to three times and makes the add-in unavailable if Outlook can't complete the evaluation. Outlook displays a message in the notification bar that the add-in is unavailable. The amount of time available for your regular expression can be modified by setting a group policy or a registry key.

    Note

    If Outlook on Windows (classic) or Outlook on Mac makes a read add-in unavailable, the read add-in becomes unavailable on the same mailbox in Outlook on the web, on mobile devices, and in new Outlook on Windows.

See also