Fix The custom dictionary is not available to be updated in Outlook

If Outlook displays a message that the custom dictionary is not available to be updated when you try to add words to the custom dictionary, then this post will help you. The custom dictionary is not available to be updated. Some additions to it may be lost.

Fix Custom Dictionary is not available in Outlook

The following solutions may help you fix this issue:

Set Custom.dic in Outlook as default.
Sign out from and sign back into your Outlook account.

Set Custom.dic in Outlook as default

Many Outlook users have reported that setting the Custom.dic as their default dictionary has fixed the issue. You can also try setting it as your default dictionary.

Follow the instructions listed below:

Launch Microsoft Outlook.
Click on the File and then click Options. This will open the Outlook Options window.
Now, select Mail from the left side and click on the “Spelling and Autocorrect” button on the right side.
You will find this button under the Compose messages section.
In the Editor Options window, select Proofing from the left side and then click on the Custom Dictionaries button on the right side.
In the Custom Dictionaries window, you will find the Roaming Custom.dic as a default dictionary.
You have to change the custom dictionary from Roaming Custom.dic to CUSTOM.DIC.
For this, select CUSTOM.DIC and click on the Change Default button on the right side.
Click on the Dictionary language drop-down menu and select the language that you have set as default in your system.
When you are done, click OK to save the changes.

Sign out and sign back in

If the method mentioned above did not fix your issue, try signing out of your Outlook account and signing back in. Some Windows users were able to fix their issues by using this method.

To sign out of the Microsoft Outlook app, click on File, then click Sign out. Close Outlook and launch it again. You will be prompted to sign in. Enter your account details and sign back in.