Outlook Shared Mailbox – How to Group Emails with Single vs Multiple Categories Applied?

Question

Outlook Shared Mailbox – How to Group Emails with Single vs Multiple Categories Applied?

Outlook Questions 0

Hi,

I'm looking for a way to better organise emails in a shared mailbox using Outlook categories.

Our team uses colour categories assigned to individuals. Many emails have a single category applied, while others have multiple categories applied to the same email.

I've found that when I sort or group emails by Category, Outlook appears to display only one category for an email, even when several categories have actually been applied. This makes it difficult to identify which emails have multiple categories assigned.

I can currently filter the mailbox by my own category, which shows:

Emails categorised only for me; and
Emails categorised for me and one or more colleagues.

However, for a housekeeping exercise, I'd ideally like to separate these into distinct groups.

What I'm trying to achieve is:

Identify emails that have only one category applied (e.g. my category only).
Identify emails that have multiple categories applied (e.g. my category plus one or more colleagues' categories).
Ideally group or filter these separately within the mailbox.

Is there a way in Outlook (desktop or web) to:

Filter based on the number of categories applied to an email?
Create a custom view that separates emails with a single category from those with multiple categories?
Use search folders, conditional formatting, or another method to achieve this?

Any suggestions would be appreciated.

Thank you.

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2 answers

Your answer

Answer 1

Hornblower409 11,955

@Outlook Questions said

Filter based on the number of categories applied to an email?

Yes, by looking for a comma (the Cat Separator in English) in the Cats field.

This is just a simple example using a Formula Field in a View. (The problem using it in Views is that you can not Group or Sort by a Formula field).

If this is anything like what you are looking for, please advise exactly where you want to use it (e.g. Search Folder) and I'll help you adapt the concept.

Formula is IIf(InStr(1,[Categories],","),"Yes","No")

And here is how to use it in a View

View -> View Settings

User's image

Outlook Questions 0 Reputation points

2026-07-23T10:55:32.89+00:00

Hello,

Thanks very much for your response.

I have tried adding the formula, which works, but does not produce the desired results.

I would like to be able to sort the mailbox by categories have each category as a stand alone category. For example, blue is a category, white is a category, blue and white is a category, blue and red is a category and so on.

Ideally, when filtered, it would look something like this:

Email 1 - blue

Email 2 - blue

Email 3 blue, red

Email 4 blue, red

Email 5 red

Email 6 - red, white

Email 7 - white

At present, I cannot find any way to organise emails containing more than one category.

Please let me know if I am making sense, or if further information is required.

Thanks again for your help.
Hornblower409 11,955 Reputation points

2026-07-23T22:29:17.1733333+00:00

Outlook Questions said

sort the mailbox by categories [and] have each category [collection] as a stand alone [Group]

Not possible. Because Cats are a special type of field (Keywords), Outlook treats them differently from any other field type.

I'm sorry, but I focused on the part of your question about detecting an item with multiple Cats and didn't look closely at your ultimate goal.

Answer Part A - Blue Only (I'll cover the Cat Collections in a separate comment)

This should be easy, but it can't be done. There is no way to get Outlook to Filter/Search for items that have only a single specific Cat. It will always include any items that have that Cat and any others.

Just to be sure that Microsoft hasn't come up with something new since I last looked at this, I spent some time with my favorite AI. It eventually gave up with:

You are completely right to call me out. I dragged you through four different broken "workarounds" before finally admitting what you already knew

And when you Groups By Cats, the MultiCats Formula Field is useless, it will always show "No". Because, from inside the Group, it only sees the Cat for that Group.
Hornblower409 11,955 Reputation points

2026-07-23T22:47:37.7066667+00:00

Outlook Questions said

blue, red ... red, white

Answer Part B - Cat Collections

You can do this, sort of. You can build a View Filter or Search Folder that shows only those items that have a specific Cat Collection.

I did my testing with a View Advanced Filter, the equivalent Search Bar query is in paren.

Here's my test data set:

The View for just Blue ( category:="Blue")

The View for Blue + Green ( category:="Blue" AND category:="Green" )

The problem is that you will have to create a separate View/Search Folder/Search Query for every combination.

If this is something you think you could manipulate into anything that would help, please advise and I'll provide instructions for building View Filters/Search Folders that can "AND" multiple conditions.

Answer 2

Dear @Outlook Questions,

I hope you’re having a good day.

I did some testing in Classic Outlook and reviewed the available Outlook documentation.

Based on my findings, Outlook supports assigning multiple categories to a message and allows filtering, grouping, and creating Search Folders based on specific category values. However, I was unable to find a built-in option that can distinguish between messages that have a single category assigned and messages that have multiple categories assigned.

In my testing, I was able to:

Filter messages by a specific category.
Group messages by category.
Create Search Folders for categorized mail.

However, I could not find a native Outlook view, filter, grouping option, or Search Folder criterion that evaluates the number of categories assigned to an item. For example, Outlook does not appear to provide conditions such as:

"Category count = 1"
"Category count > 1"
"Has multiple categories"

As a result, I was not able to separate messages into "single-category" versus "multi-category" groups using only Outlook's built-in features.

I also reviewed Outlook custom field documentation. While Outlook supports custom fields and custom properties, I did not find documentation describing a built-in field that exposes the number of categories assigned to a message for use in views, filters, or Search Folders.

Based on both the available documentation and my testing, this appears to be a product limitation rather than a configuration issue with the shared mailbox.

For reference:

I hope this helps clarify the current behavior. If another community member has found a supported approach that achieves this using only Outlook's built-in features, I'd be interested to learn about it as well.

Since your scenario is a valid use case for shared mailbox management, you may also want to submit feedback directly to the Outlook product team. User feedback helps the team evaluate demand for new features and improvements.

You can submit feedback from Classic Outlook by selecting Help > Feedback, or through the Outlook feedback portal

If you do submit feedback, it may be helpful to describe the ability to distinguish between messages with a single category and messages with multiple categories, and to request support for filtering, grouping, or Search Folder criteria based on the number of categories assigned to an item.

I hope this information helps point you in the right direction. Please feel free to reply below if you have any update or further concern.

Warm regards,

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