Outlook’s spell check is one of those features you only notice when it stops working — usually right before you send an important email. Unlike standalone applications that bundle their own proofing tools, Microsoft Outlook borrows its spell check engine directly from Microsoft Word. That single dependency is the root cause of most spell check failures, and it means that fixing the problem often involves looking in places you might not expect. Whether your red underlines have disappeared, nothing gets flagged before sending, or the wrong language keeps being applied, this guide walks through every reliable fix in a logical order.
\n\n\n\nCommon Reasons Outlook Spell Check Stops Working
\n\n\n\n- \n
- Spell check is simply turned off in Outlook settings — the most common cause, and the easiest to fix \n\n\n\n
- The proofing language is set incorrectly — if Outlook thinks you are writing in a language with no dictionary installed, no errors will ever be flagged \n\n\n\n
- Microsoft Word is not installed — Outlook uses Word’s proofing engine; if Word isn’t part of your Office installation, spell check cannot function \n\n\n\n
- A faulty or conflicting add-in — COM add-ins can interfere with Outlook’s core functions; third-party CRM or security plugins are frequent offenders \n\n\n\n
- A corrupt Office installation — damaged registry entries or missing Office files will break proofing tools across all Office applications \n\n\n\n
- A corrupt or oversized custom dictionary — the file that stores words you have manually added can become corrupted, causing the proofing engine to stall \n
Fix 1 — Enable Spell Check in Outlook Settings
\n\n\n\nStart here before anything else. Outlook has its own spell check toggle that is completely separate from Word’s settings, and it can get switched off without any obvious warning.
- \n
- Open Outlook and go to File > Options. \n\n\n\n
- Click Mail in the left-hand panel. \n\n\n\n
- Scroll down to the Compose messages section. \n\n\n\n
- Tick “Always check spelling before sending” — this gives you a final safety net every time you hit Send. \n\n\n\n
- Click Spelling and Autocorrect, then select Proofing. Make sure “Check spelling as you type” is ticked so red underlines appear in real time. \n\n\n\n
- Click OK to save, close and reopen Outlook, then type a deliberate spelling mistake to test. \n
Fix 2 — Set the Correct Proofing Language
\n\n\n\nOutlook can silently switch the proofing language for a message to one that either has no installed dictionary or has spell checking explicitly disabled. This is particularly common if you receive a lot of emails in other languages or have recently changed your Windows display language.
\n\n\n\n- \n
- Open a new email compose window. \n\n\n\n
- In the ribbon, click the Review tab. \n\n\n\n
- Click Language, then Set Proofing Language. \n\n\n\n
- Select English (United Kingdom) from the list. \n\n\n\n
- Make absolutely sure the “Do not check spelling or grammar” checkbox is unchecked. If this box is ticked, Outlook will never flag a single error. \n\n\n\n
- Click Set As Default if you want this applied to all future messages, then click OK. \n
Note that the proofing language can also be set at a per-paragraph level inside a message. If spell check works in some parts of an email but not others, select all the text, open the language dialog again and apply your language to the full selection.
\n\n\n\nFix 3 — Check Microsoft Word Is Installed
\n\n\n\nThis catches a lot of people off guard. Outlook delegates its entire spell check operation to Word’s proofing engine, which means Word must be installed on the same machine. If your Office licence includes Outlook but not Word — for example a standalone Outlook subscription or certain Microsoft 365 Business plans — spell check will simply not work.
\n\n\n\nOpen the Start menu and search for Word. If it does not appear as an installed application, Word is missing from your installation. There is no workaround — you need a Microsoft 365 plan that includes Word for spell check to function in Outlook. This is one area where Outlook behaves very differently to Word’s own spell check, which bundles its proofing tools as part of the Word install itself.
Fix 4 — Disable Outlook Add-ins
\n\n\n\nCOM add-ins run inside the Outlook process and can interfere with core functionality. Disabling them temporarily is a reliable way to isolate whether a plugin is causing the spell check failure.
\n\n\n\n- \n
- Go to File > Options > Add-ins. \n\n\n\n
- At the bottom of the screen, set the Manage dropdown to COM Add-ins and click Go. \n\n\n\n
- Uncheck every add-in in the list to disable them all, then click OK. \n\n\n\n
- Restart Outlook and test spell check by typing a deliberate error. \n\n\n\n
- If spell check now works, re-enable the add-ins one at a time — restarting Outlook each time — until the problem returns. The last add-in you re-enabled is the culprit. \n
Fix 5 — Clear and Rebuild the Custom Dictionary
\n\n\n\nOver time the custom dictionary file — which stores words you have manually added — can grow large or become corrupted. Deleting it forces Outlook to create a clean replacement.
\n\n\n\n- \n
- Go to File > Options > Mail and click Spelling and Autocorrect. \n\n\n\n
- Click Proofing, then select Custom Dictionaries. \n\n\n\n
- Select CUSTOM.DIC and click Edit Word List to review and delete individual entries. \n\n\n\n
- Alternatively, close Outlook and navigate to
C:\\Users\\[YourName]\\AppData\\Roaming\\Microsoft\\UProof\\. Rename CUSTOM.DIC to CUSTOM.DIC.bak to preserve your old entries. \n\n\n\n - Reopen Outlook — a fresh CUSTOM.DIC will be created automatically. \n
Fix 6 — Run a Microsoft Office Repair
\n\n\n\nIf none of the above has resolved the issue, a corrupt Office installation is the most likely remaining cause. Problems like this sometimes surface after a failed update — if that sounds familiar, you may also want to check our guide on Outlook not working after a Windows or Office update.
\n\n\n\n- \n
- Close all Office applications completely. \n\n\n\n
- Open Control Panel and navigate to Programs > Programs and Features. \n\n\n\n
- Find Microsoft 365 in the list, right-click it and select Change. \n\n\n\n
- Choose Quick Repair first — this runs locally and completes in a few minutes. \n\n\n\n
- If Quick Repair does not fix the problem, run the process again and choose Online Repair instead. \n\n\n\n
- Restart your computer after the repair completes and test Outlook spell check again. \n
Fix 7 — Check Autocorrect Isn’t Overriding Spell Check
\n\n\n\nAutocorrect and spell check are separate features but share the same settings area and can conflict. If Autocorrect is set to silently correct words as you type, you may not realise a word was flagged and fixed — making it appear as though spell check is not running when it actually is.
\n\n\n\nGo to File > Options > Mail > Spelling and Autocorrect > AutoCorrect Options. Review the AutoCorrect tab and look for any entries that might be silently replacing words you want spell check to catch. If Outlook still feels sluggish even after resolving the spell check issue, our guide on Outlook running slow covers the common causes — performance problems and proofing failures sometimes share the same underlying root.
\n\n\n\nFrequently Asked Questions
\n\n\n\nDoes spell check work in Outlook without Word installed?
\n\n\n\nNo. Outlook does not include its own proofing engine and relies entirely on Microsoft Word to provide spell check. If Word is not installed on your device, Outlook will have no spell checking capability. There is no supported workaround — you need a Microsoft 365 plan that includes Word.
\n\n\n\nWhy is spell check not catching certain words even when it’s turned on?
\n\n\n\nThe word may already be in your custom dictionary from a previous session. The text may also be formatted with a language that has no dictionary installed, or with the “Do not check spelling” flag applied at the paragraph level. Select the specific text that is not being checked, open Review > Language > Set Proofing Language and reapply your preferred language.
\n\n\n\nHow do I add a word to the Outlook dictionary?
\n\n\n\nWhen spell check underlines a word in red, right-click it and select Add to Dictionary. Alternatively, add words manually via File > Options > Mail > Spelling and Autocorrect > Proofing > Custom Dictionaries > Edit Word List. Words added this way are stored per Windows user account and will not carry over to another machine.
\n\n\n\nSpell check works in new emails but not in replies — how do I fix this?
\n\n\n\nThis is a known Outlook behaviour. Outlook does not spell check the original quoted text in a reply, which is correct. However, if spell check is not running on your typed reply text, the proofing language may have been inherited from the quoted section below. Select only the text you have typed, then go to Review > Language > Set Proofing Language and reapply English (United Kingdom). Click Set As Default to prevent this from happening on every reply.
\n\n
