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Quick Answer

Right-click an email, hover over Categorize, and select a color to tag it. To set a reminder, right-click the Flag icon next to the email, select Add Reminder, and choose a date and time.

How to Use Outlook Categories and Flags to Stay Organized ​

Applies to: Microsoft Outlook (Desktop, Web, Mobile)
Article Type: How-To
Last Updated: 2026-05-19

Summary ​

This article shows you how to use color categories and follow-up flags in Outlook to visually organize your emails, calendar events, contacts, and tasks. Categories let you tag items with color-coded labels (e.g., "Project Alpha," "Urgent," "Waiting for Response"), while flags add reminders so important items do not slip through the cracks.

Prerequisites ​

  • A Microsoft 365 account with Outlook access.
  • Outlook Desktop (Classic or New), Outlook on the Web, or Outlook Mobile.

Instructions ​

1. Understand Categories vs. Flags ​

FeatureCategoriesFlags
PurposeColor-coded labels for grouping and filteringReminders and follow-up tracking
Works onEmails, calendar events, contacts, tasksEmails only
Visual indicatorColored square next to the itemFlag icon next to the item
Reminder support❌✅ (set a due date and reminder)
Multiple per item✅ (an email can have multiple categories)❌ (one flag per email)
Appears in To Do❌✅ (flagged emails sync to Microsoft To Do)

Tip: Use categories for classification ("what type of thing is this?") and flags for action ("I need to follow up on this").

2. Create and Customize Categories ​

Outlook Desktop (Classic) ​

  1. Go to the Home tab and click Categorize > All Categories.
  2. The Color Categories dialog shows the default categories (each with a color).
  3. To rename a category: select it and click Rename. Give it a meaningful name (e.g., "Project Alpha," "Client Follow-Up," "Read Later").
  4. To change the color: select the category and click a color from the palette.
  5. To add a new category: click New, enter a name, choose a color, and optionally assign a shortcut key.
  6. Click OK to save.

Outlook on the Web ​

  1. Click the Settings gear icon (top right) > View all Outlook settings.
  2. Go to General > Categories.
  3. Click + Create category, enter a name, and choose a color.
  4. Click Save.

New Outlook (Desktop) ​

  1. Click the Settings gear icon > Categories.
  2. Create, rename, or delete categories.

3. Apply a Category to an Email ​

  1. Select the email (or open it).
  2. Click Categorize in the ribbon (or right-click the email > Categorize).
  3. Select the category you want to apply.
  4. The colored category tag appears next to the email in your message list.
  5. To apply multiple categories, repeat the process — an email can have as many categories as you need.

Tip: Assign keyboard shortcuts to your most-used categories for instant tagging. In the All Categories dialog, assign shortcuts like Ctrl + F2, Ctrl + F3, etc.

4. Apply a Category to Calendar Events or Contacts ​

Categories are not limited to emails — you can apply them to calendar events and contacts too.

Calendar Events ​

  1. Open the calendar event.
  2. Click Categorize in the event ribbon.
  3. Select a category. The event appears in the calendar with the category's color.

Contacts ​

  1. Open a contact.
  2. Click Categorize and select a category.
  3. You can then filter your contact list by category.

5. Filter and Sort by Category ​

Once you have categorized your emails, you can filter your inbox to show only items with a specific category.

Outlook Desktop ​

  1. In the message list, click View > View Settings > Filter (or Sort).
  2. Use the Categories criteria to filter by a specific category.
  3. Alternatively, click the Categories column header in the message list to sort all emails by category.

Outlook on the Web ​

  1. Click the Filter button at the top of the message list.
  2. Select a category from the filter dropdown.

Search by Category ​

  1. In the Outlook search bar, type category:"Project Alpha" (replace with your category name).
  2. Outlook shows only items tagged with that category.

6. Flag an Email for Follow-Up ​

Flags add a visual reminder and sync with Microsoft To Do, so flagged emails appear in your task list.

  1. In your inbox, hover over the email.
  2. Click the flag icon that appears on the right side of the message row.
  3. The email is flagged with a default "Follow up" reminder.
  4. The flagged email now appears in Microsoft To Do under the Flagged email list.

Set a Specific Due Date ​

  1. Right-click the flag icon on the email.
  2. Select a timeframe:
    • Today — Due today, reminder at end of day.
    • Tomorrow — Due tomorrow.
    • This Week — Due by end of the current week.
    • Next Week — Due by end of next week.
    • Custom — Set a specific start date, due date, and reminder time.

Mark as Complete ​

  1. Click the flag icon again to mark the follow-up as complete.
  2. The flag changes to a checkmark, and the task is marked as done in To Do.

7. Set Up a Quick Click Flag ​

If you flag emails frequently, set a default flag so a single click applies your preferred timeframe.

  1. In Outlook Desktop: right-click the flag column header and select Set Quick Click.
  2. Choose the default flag type (e.g., Today, Tomorrow, This Week).
  3. Click OK. Now a single click on the flag icon applies that default.

8. Combine Categories and Flags for a Complete System ​

For maximum organization, use both features together:

Email TypeCategoryFlag
Client request requiring a response"Client" (blue)Flag for Today
Project update — read later"Project Alpha" (green)No flag (informational)
Waiting for someone else's reply"Waiting" (yellow)Flag for Next Week
Urgent issue from management"Urgent" (red)Flag for Today with reminder
Newsletter to review when free"Read Later" (purple)No flag

Troubleshooting ​

TIP

If you are new to categories, start with 5–7 categories that match your actual workflow (e.g., by project, client, or action type). Too many categories creates overhead — keep it simple and consistent.

Symptom / ErrorPotential CauseSolution
Categories do not sync between devicesCategory names differ between desktop and webCreate categories in Outlook on the Web — these sync to all devices. Desktop-only categories may not sync.
Flagged emails do not appear in To DoTo Do is not connected to your Outlook accountOpen Microsoft To Do and sign in with the same work account. Flagged emails should appear under Flagged email.
Category colors look different on web vs. desktopColor palettes differ slightly between clientsChoose colors that are distinct enough to be recognizable across all platforms.
Cannot see the Categories columnColumn is hidden in the message listRight-click the column headers in Outlook Desktop and check Categories to show the column.
Flag reminder does not appearReminder time has passed or reminders are disabledRight-click the flag > Custom and set a future reminder time. Check File > Options > Advanced > Reminders to ensure they are enabled.