Exchange Online - Handling Migrated Categories

Using the “Categories” in Outlook is an easy way to group/manage emails, calendar items, tasks, etc. - see the Microsoft Guide here for details https://support.microsoft.com/en-us/office/create-and-assign-color-categories-a1fde97e-15e1-4179-a1a0-8a91ef89b8dc

If you have been using categories on Exchange 2013, when you are migrated to the UIS Exchange Online email service which also has its own distinct list of categories, those categories will merge.

For example, if you have an existing Exchange 2013 red category & called it “Urgent”, once the mailbox is migrated, any emails, calendar items, tasks etc. using the red category, will have “Urgent”, as well as the new UIS Exchange Online red category of “Important”, see below:

existing & new red categories combined

We therefore recommend:

All existing categories have distinct names that are different to the new UIS Exchange Online categories. If necessary, rename categories prior to migration by maybe adding a prefix like “OLD-<name of category>” or take a screenshot of your existing Exchange 2013 categories for reference.
After the mailbox has been migrated & categories have been merged, login to the web version of Outlook, using this address Outlook
Go to Settings (top-right of the screen) and then to the bottom & click on View All Outlook Settings.

Then go to General >> Categories

For those unwanted categories you do not need, click on the bin to delete them, or for those you wish to keep and may need to rename, click on the pencil to edit.
Once you have updated the category list to your preferences, log out of the web version of Outlook & then open the Outlook application on your device (if you use it). This will allow the web version and Outlook application to synchronise to make sure they both have the correct category list.

There are a few points to note:

This issue only occurs with categories of a similar colour
Any emails, calendar items, tasks etc. that have been migrated & had a subsequent similar category colour deleted, you will see these items will appear to have 2 categories:
- 1 in white as it’s the one that was deleted (which could still be used to filter/manage with rules etc.) and
- 1 that was migrated & is correct
Once you create new emails, calendar items, tasks etc. you will no longer see duplicate categories applied to the new items
At no point should you run “Upgrade to Color Categories” button as this will re-compile the categories list based on what is in your mailbox, which includes the categories that have been deleted/show as white.