Spell check in Outlook 365 is on by default, but you control when it runs and what it flags

Outlook 365 checks your spelling as you type in the message body — you'll see red squiggly lines under words it doesn't recognize. Unlike some email programs, Outlook doesn't check the subject line or recipient fields automatically. The spell checker uses the language you've set in Windows or Office, so if you write in multiple languages, you may need to switch your proofing language mid-message or turn off checking for specific words you use often.

If you don't see red squiggles under misspelled words, spell check may be turned off in your settings, or you may be using a version that doesn't support it in your current view. The steps to fix this depend on whether you're using Outlook on the web, Outlook on your desktop, or Outlook on a phone.

Key Takeaways

  • Spell check runs automatically in Outlook 365 message bodies as you type, marked by red squiggly lines under unrecognized words.
  • You can turn spell check on or off in Outlook desktop settings under File > Options > Mail > Spelling, and in Outlook on the web under Settings > Mail > Compose and reply.
  • Right-click any red-underlined word to see suggested corrections, add it to your dictionary, or ignore it for the rest of your session.
  • Outlook does not spell-check subject lines or recipient fields by default, only the message body.
  • If you write in multiple languages, you can set a proofing language for each message or add words to a custom dictionary so Outlook stops flagging them.

Turn spell check on or off in Outlook desktop

Open Outlook and go to File in the top left. Click Options, then select Mail from the left sidebar. Scroll down to the Spelling section. You'll see a checkbox next to "Always suggest replacements for misspelled words" — this is checked by default. If you uncheck it, Outlook will still underline misspelled words but won't offer suggestions when you right-click them.

Below that, you can also check "Ignore words in UPPERCASE" and "Ignore words with numbers" if you use acronyms or product codes that Outlook keeps flagging. Once you've made your changes, click OK at the bottom of the window. The changes take effect when ready in new messages you compose.

Turn spell check on or off in Outlook on the web

Log into your Outlook account at outlook.office.com. Click the gear icon in the top right corner and select View all Outlook settings. Go to Mail > Compose and reply. Under the "Spelling" section, toggle the switch next to "Check spelling as you type" on or off. If the toggle is on, you'll see red squiggles in the message body as you type. If it's off, no spell checking happens.

Outlook on the web does not offer as many spelling options as the desktop version — you can only turn checking on or off, not customize what gets ignored. If you need more control, use the desktop version of Outlook instead.

Right-click to fix or ignore a misspelled word

When you see a red squiggly line under a word, right-click it. A menu will appear with three types of options: suggested corrections at the top, an option to "Add to Dictionary" in the middle, and "Ignore All" at the bottom. Click any suggested word to replace the misspelled word when ready. Click "Add to Dictionary" if the word is correct but Outlook doesn't recognize it — Outlook will stop flagging it in any message you write going forward.

Click "Ignore All" if you want Outlook to stop flagging that word for the rest of your current session only. Once you close and reopen Outlook, the word will be flagged again if you misspell it. If you use a word regularly and don't want to add it to your main dictionary, "Ignore All" is a good middle ground.

Add words to your custom dictionary

When you click "Add to Dictionary" on a word, Outlook saves it to a file called CUSTOM.DIC. This file lives on your computer and travels with you if you sign into Outlook on another device — the custom dictionary is tied to your Microsoft account, not to a specific computer. If you want to add multiple words at once without misspelling them first, you can edit the custom dictionary directly in Outlook desktop.

Go to File > Options > Mail > Spelling and click the button labeled "Custom Dictionaries" (this button only appears in Outlook desktop, not on the web). A window will open showing your CUSTOM.DIC file. Click Edit Word List, then type each word you want to add on a new line. Click OK when you're done. Outlook will stop flagging those words in any message you write.

Set a proofing language for messages in other languages

If you write in English and Spanish, for example, Outlook will flag Spanish words as misspelled if your proofing language is set to English. To fix this, select the text in your message that's in a different language. Go to Review in the ribbon at the top, then click Language > Set Proofing Language. A window will open showing available languages. Select the language you're writing in and click OK. Outlook will now check spelling for that text using the rules of the language you selected.

If you switch languages mid-message, you'll need to repeat this step for each section. Alternatively, you can add Spanish words to your custom dictionary so Outlook stops flagging them no matter what language your proofing setting is. This works well if you use a few words from another language regularly but write mostly in English.

Spell check doesn't work in subject lines or recipient fields

Outlook 365 only checks spelling in the message body by default. If you misspell something in the subject line or in the "To:" field, Outlook won't flag it. This is a deliberate design choice — subject lines and recipient names are treated differently because they're metadata rather than message content. If you want to catch spelling errors in your subject line, read it over before you send, or copy it into the message body, run spell check there, then copy it back.

Some third-party add-ins for Outlook can extend spell checking to subject lines and other fields, but they require separate installation and are not built into Outlook 365. For most users, checking the subject line manually takes less time than installing an add-in.

Frequently Asked Questions

Why am I not seeing red squiggles under misspelled words?

Spell check may be turned off in your settings. In Outlook desktop, go to File > Options > Mail > Spelling and make sure "Always suggest replacements for misspelled words" is checked. In Outlook on the web, go to Settings > Mail > Compose and reply and toggle "Check spelling as you type" on. If you're using Outlook in a read-only view or composing in a plain-text format, spell check may not appear.

Can I spell-check before I send, instead of as I type?

Outlook 365 doesn't have a "check now" button like older versions did. Spell check runs automatically as you type. If you prefer to review spelling all at once before sending, you can turn off "Always suggest replacements" in your settings so Outlook still underlines errors but doesn't interrupt your typing with suggestions.

What if Outlook keeps flagging a word that's spelled correctly?

Right-click the word and click "Add to Dictionary." Outlook will stop flagging it in any message you write. If it's a proper noun or brand name you use often, adding it to your dictionary is the fastest solution. You can also use "Ignore All" if you only want to ignore it in your current message.

Does spell check work on my phone or tablet?

Outlook on iPhone and Android relies on your device's built-in spell checker, not Outlook's own spell check. Your phone or tablet will underline misspelled words using its own dictionary. You can't customize Outlook's spell check settings on mobile — you can only use what your device offers.

Can I use spell check in multiple languages at the same time?

You can set different proofing languages for different parts of the same message by selecting text and using Review > Language > Set Proofing Language. However, Outlook can only check one language at a time per selection. If you write in two languages frequently, adding words from both to your custom dictionary is often easier than switching languages mid-message.