Categories vs. Unique Arguments: Benefits & Limitations

August 31, 2021
Written by
Devon Montgomery
Opinions expressed by Twilio contributors are their own

Categories vs. Unique Arguments: Benefits & Limitations

You created your Twilio SendGrid account, authenticated your domain, added a dedicated IP address, and started sending. Now, you’re wondering how you can dive into the analytics of your email events a little further and read the story behind the numbers.

As an Onboarding Engineer on Twilio SendGrid’s team, I’ve spoken with hundreds of customers who know the metrics they want to track but aren’t exactly sure how they can use the tools available within Twilio SendGrid. 

In this article, I’ll dive into how you can organize your email analytics using categories and unique arguments as well as the benefits and limitations of those tools.

Prepare your email data

Before you get started with unique arguments and category tracking, it’s important to decide how you’ll be organizing your data and what metrics you’ll lean on. Here are a couple of tips to get started.

Segment your target audience

Different email types provide very distinct metrics in terms of performance. So, deciding how you would like to segment your audience is the first step in determining which tools to use within SendGrid.

Are you sending marketing or transactional emails? Are you sending a batch of emails for a tradeshow coming up? Is this a webinar for lead generation? 

It’s important to determine your target audience from both a content and analytics perspective. For example, you might want to segment your webinar emails from the blast of 100,000 welcome emails that were just delivered. 

Determine your preferred email metrics

Before you can slice and dice the data with unique arguments and categories, you’ll need to decide what a successful email campaign looks like. Will you look at open rate or click through rate? Will you factor in the delivery rate?

If you haven’t determined what metrics you’re looking to evaluate for performance, this resource on email metrics will help you get up to speed on what customers are typically looking for (likes, opens, clicks, blocks, etc.).

Categories vs. unique arguments

Now that you have prepped your email data, let’s take a look at how you can dig into the details of your email analytics.

Twilio SendGrid's Aggregate Stats Dashboard and Event Webhook allow you to track the performance of your campaigns using categories and unique arguments. A common question we receive from customers is, "What's the difference between a category and a unique argument?" 

While the two are similar in terms of functionality, categories and unique (also known as custom) arguments have specific use cases for tracking your email lists.

To help you decide which tracking tool is the right one for your program, ask yourself the following questions:
Questions CategoriesUnique Arguments
Are you using Marketing Campaigns, Email API, or both?Better suited for Marketing CampaignsBetter suited for Email API
Are you tracking how each campaign is performing or tracking individual recipients?Tracks campaign performanceTracks individual recipients
Are you tracking your data externally or using Twilio SendGrid’s user interface?Uses Twilio SendGrid’s user interfaceProvide external tracking via the event webhook

Tracking data with categories 

You can use categories to analyze your different campaigns, but know there are limitations. Use categories to determine how, for example, your webinar emails are performing versus your upcoming trade show. 

Too many categories can slow down your Twilio SendGrid user interface, so there is a limit of 100 categories per user. They can’t be deleted once they’re created, so be strategic when determining mail segmentation.   
Categories have a daily usage limit of 100/day per user (1000/day for paid accounts).

Use Case

  • Imagine your company has a huge event approaching in a couple of months (conference, lead generation, etc.). Your sales or marketing team is prepared to send a batch campaign to thousands of recipients, but you'd like to track the performance metrics of these campaigns. 


  • Categories allow you to track things like marketing messages vs. transactional messages in the same batch.
  • Twilio SendGrid has categorical dashboards available to you out of the box, so aggregate stats that are specifically related to categories can easily be analyzed at a high level.
  • You can use that information to peruse different types of categories and see the stats only associated with that category.


  • Categories have a daily usage limit of 100/day per user (1000/day for paid accounts).
  • This limitation is in place to provide you the best experience while using Twilio SendGrid because too many categories slow down the UI.

Tracking data with unique arguments

Use unique arguments to track individual recipients or analyze data externally.
Compared to categories, unique arguments are limitless.
If you’re primarily using the Email API, these are better suited, as category usage could quickly add up. 

Use Case

  • You’re planning on using Twilio SendGrid's event webhook to consume open, click, and spam report data. You need to pass an argument that the email is “testing” or “production.” You would like to pass an argument that filters for “production only” events.


  • Compared to categories, unique arguments are limitless.
  • Unique arguments are advantageous if there is a need to track data on a more granular level.
  • You can provide a key value pair attached to recipients (Ex: customerID: 4567). This allows you to customize your tracking parameters per recipient however you'd like.


  • Unfortunately, you cannot query unique argument information within the UI.
  • Like we mentioned in the use case, the event webhook will be the best tool to use for external tracking. This will require more development work on your end.

Recap: Categories and unique arguments

To recap, categories are better suited to view overall campaign performance while unique arguments are great for tracking the engagement of individual recipients. 

Whether you decide to use categories, unique arguments, or both, depends on your use case. If you’re not sure what you should be tracking, go back to the basics and evaluate how you’re segmenting your campaigns and your markers for a successful campaign. 

For help understanding how your email campaigns are performing, Twilio SendGrid has a great overview of statistics that provides details on how your email is being used. Feel free to reach out to our support team or check out the categories docs article for any additional questions on setting up these features for your email project.

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