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Use regular expression activation rules to show a mail app in Outlook

apps for Office

Learn how to use regular expressions to specify the criteria for a mail app to be relevant in a read scenario and that Outlook should display the app in the UI.

Last modified: May 01, 2015

Applies to: apps for Office | Office Add-ins | Outlook

Learn more about supported hosts and other requirements.

Note Note

The name "apps for Office" is changing to "Office Add-ins". During the transition, the documentation and the UI of some Office host applications and Visual Studio tools might still use the term "apps for Office". For details, see New name for apps for Office and SharePoint.

In this article
Support for regular expressions
ItemHasRegularExpressionMatch rule
ItemHasKnownEntity rule
Using regular expression results in code
Additional resources

You can specify regular expression rules to have a mail app activated in read scenarios - when the user views a message or appointment in the Reading Pane or inspector, Outlook evaluates regular expression rules to determine if it should activate your mail app. Outlook does not evaluate these rules when the user is composing an item. There are also other scenarios where Outlook does not activate mail apps, for example, items protected by Information Rights Management (IRM) or in the Junk Email folder. For more information, see Items supporting activation.

You can specify a regular expression as part of an ItemHasRegularExpressionMatch rule or ItemHasKnownEntity rule in the app XML manifest. Outlook evaluates regular expressions based on the rules for the JavaScript interpreter used by the browser on the client computer. Outlook supports the same list of special characters that all XML processors also support. The following table lists these special characters. You can use these characters in a regular expression by specifying the escaped sequence for the corresponding character, as described in the following table.



Escaped sequence to use


Double quotation mark








Less-than sign



Greater-than sign


An ItemHasRegularExpressionMatch rule is useful in controlling activation of a mail app based on specific values of a supported property. The ItemHasRegularExpressionMatch rule has the following attributes.

Attribute name



Specifies the name of the regular expression so that you can refer to the expression in the code for your app.


Specifies the regular expression that will be evaluated to determine whether the mail app should be shown.


Specifies the name of the property that the regular expression will be evaluated against. The allowed values are BodyAsHTML, BodyAsPlaintext, SenderSMTPAddress, and Subject.

If you specify BodyAsHTML, Outlook applies the regular expression only if the item body is HTML, and otherwise Outlook returns no matches for that regular expression. Because appointments are always saved in Rich Text Format, a regular expression that specifies BodyAsHTML does not match any strings in the body of appointment items.

If you specify BodyAsPlaintext, Outlook always applies the regular expression on the item body.


Specifies whether to ignore case when matching the regular expression specified by RegExName.

Best practices for using regular expressions in rules

Pay special attention to the following when you use regular expressions:

  • If you specify an ItemHasRegularExpressionMatch rule on the body of an item, the regular expression should further filter the body and should not attempt to return the entire body of the item. Using a regular expression such as .* to attempt to obtain the entire body of an item does not always return the expected results.

  • The plain text body returned on one browser can be different in subtle ways on another. If you use an ItemHasRegularExpressionMatch rule with BodyAsPlaintext as the PropertyName attribute, test your regular expression on all the browsers that your app supports.

    Because different browsers use different ways to obtain the text body of a selected item, you should make sure that your regular expression supports the subtle differences that can be returned as part of the body text. For example, some browsers such as Internet Explorer 9 uses the innerText property of the DOM, and others such as Firefox uses the .textContent() method to obtain the text body of an item. Also, different browsers may return line breaks differently: a line break is "\r\n" on Internet Explorer, and "\n" on Firefox and Chrome. For more information, see W3C DOM Compatibility - HTML.

  • The HTML body of an item is slightly different between an Outlook rich client, and Outlook Web App or OWA for Devices. Define your regular expressions carefully. As an example, consider the following regular expression used in an ItemHasRegularExpressionMatch rule with BodyAsHTML as the PropertyName attribute value:


    A rule with this regular expression would match the string "http-equiv="Content-Type" which exists in the HTML body of an item in an Outlook rich client, as part of the following META tag:

    <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=us-ascii">

    The same rule does not return this match in Outlook Web App and OWA for Devices because the HTML body in these hosts does not include that META tag. This can affect whether the mail app is activated appropriately for the various Outlook clients. In this example, use the following regular expression instead:

  • Depending on the host application, type of device, or property that a regular expression is being applied on, there are other best practices and limits for each of the hosts that you should be aware of when designing regular expressions as activation rules. See Limits for activation and JavaScript API for mail apps in Outlook for details.


The following ItemHasRegularExpressionMatch rule activates the mail app whenever the sender's SMTP email address matches "@contoso", regardless of uppercase or lowercase characters.

<Rule xsi:type="ItemHasRegularExpressionMatch" 

The following is another way to specify the same regular expression using the IgnoreCase attribute.

<Rule xsi:type="ItemHasRegularExpressionMatch" 

The following ItemHasRegularExpressionMatch rule activates the mail app whenever a stock symbol is included in the body of the current item.

<Rule xsi:type="ItemHasRegularExpressionMatch" 

An ItemHasKnownEntity rule activates a mail app based on the existence of an entity in the subject or body of the selected item. The KnownEntityType type defines the supported entities. Applying a regular expression on an ItemHasKnownEntity rule provides the convenience where activation is based on a subset of values for an entity (for example, a specific set of URLs, or telephone numbers with a certain area code).

Note Note

Outlook can extract entity strings in only English regardless of the default locale specified in the manifest.

Only messages but not appointments support the MeetingSuggestion entity type.

You cannot extract entities from items in the Sent Items folder, nor can you use an ItemHasKnownEntity rule to activate a mail app for items in the Sent Items folder.

The ItemHasKnownEntity rule supports the attributes in the following table. Note that while specifying a regular expression is optional in an ItemHasKnownEntity rule, if you choose to use a regular expression as an entity filter, you must specify both the RegExFilter and FilterName attributes.

Attribute name



Specifies the type of entity that must be found for the rule to evaluate to true. Use multiple rules to specify multiple types of entities.


Specifies a regular expression that further filters instances of the entity specified by EntityType.


Specifies the name of the regular expression specified by RegExFilter, so that it is subsequently possible to refer to it by code.


Specifies whether to ignore case when matching the regular expression specified by RegExFilter.


The following ItemHasKnownEntity rule activates the mail app whenever there is a URL in the subject or body of the current item, and the URL contains the string "youtube", regardless of the case of the string.

<Rule xsi:type="ItemHasKnownEntity" 

You can obtain matches to a regular expression by using the following methods on the Appointment object or Message object for the current item:

  • getRegExMatches returns matches in the current item for all regular expressions specified in ItemHasRegularExpressionMatch and ItemHasKnownEntity rules of the mail app.

  • getRegExMatchesByName(name) returns matches in the current item for the identified regular expression specified in an ItemHasRegularExpressionMatch rule of the mail app.

  • getFilteredEntitiesByName(name) returns entire instances of entities that contain matches for the identified regular expression specified in an ItemHasKnownEntity rule of the mail app.

When the regular expressions are evaluated, the matches are returned to your mail app in an array object. For getRegExMatches, that object has the identifier of the name of the regular expression.

Note Note

An Outlook rich client does not return matches in any particular order in the array. Also, you should not assume the Outlook rich client to return matches in the same order in this array as Outlook Web App or OWA for Devices, even when you run the same mail app on each of these clients on the same item in the same mailbox. For other differences in processing regular expressions between an Outlook rich client and Outlook Web App or OWA for Devices, see Limits for activation and JavaScript API for mail apps in Outlook.


The following is an example of a rule collection that contains an ItemHasRegularExpressionMatch rule with a regular expression named videoURL.

<Rule xsi:type="RuleCollection" Mode="And">
    <Rule xsi:type="ItemIs" ItemType="Message"/>
    <Rule xsi:type="ItemHasRegularExpressionMatch" RegExName="VideoURL" RegExValue="http://www\.youtube\.com/watch\?v=[a-zA-Z0-9_-]{11}" PropertyName="Body"/>

The following example uses getRegExMatches of the current item to set a variable videos to the results of the preceding ItemHasRegularExpressionMatch rule.

var videos = Office.context.mailbox.item.getRegExMatches().videoURL;

Multiple matches are stored as array elements in that object. The following code example shows how to iterate over the matches for a regular expression named reg1 to build a string to display as HTML.

function initDialer() 
    var myEntities;
    var myString;
    var myCell;
    myEntities = _Item.getRegExMatches();

    myString = "";
    myCell = document.getElementById('dialerholder');
    // Loop over the myEntities collection.
    for (var i in myEntities.reg1) {
        myString += "<p><a href='callto:tel:" + myEntities.reg1[i] + "'>" + myEntities.reg1[i] + "</a></p>";
    myCell.innerHTML = myString;

The following is an example of an ItemHasKnownEntity rule that specifies the MeetingSuggestion entity and a regular expression named CampSuggestion. Outlook activates the mail app if it detects that the currently selected item contains a meeting suggestion, and the subject or body contains the term "WonderCamp".

<Rule xsi:type="ItemHasKnownEntity" 

The following code example uses getFilteredEntitiesByName(name) of the current item to set a variable suggestions to get an array of detected meeting suggestions for the preceding ItemHasKnownEntity rule.

var suggestions = Office.context.mailbox.item.getFilteredEntitiesByName(CampSuggestion);
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