In the Outlook Options dialog, click Mail from left pane, and go to the Compose messages section, check Always check spelling before sending checkbox. Outlook for Mac automatically checks for potential spelling and grammatical errors as you type, and you can use your keyboard and VoiceOver, the built-in macOS screen reader, to go through the errors and fix them. Need instructions on how to check spelling and grammar in Outlook, but not using a screen reader? Follow with me and tick along the trail File Options Mail under Compose Message, select Always check spelling before sending click; If you are working on Outlook 2007, then you can follow the method given below. For MS Outlook 2007 users: Tick on Tools Options click Spelling tab select Always Check Spelling before Sending. Now, when we click “Send” on an email with a spelling error, Microsoft Outlook will pick it up and give us the chance to change it. If you spot something in the email that the spell checker hasn’t picked up and you want to change it, click “Cancel.” This will open a dialogue box that lets you cancel sending the email. In Outlook 2016 for Windows, there is an option to always check spelling before sending an e-mail message. However, Outlook 2016 for Mac does not have this option, instead it checks for spelling errors as you type. Given this situation, we suggest you feedback your requirement to our related team via the link below.
How to check spelling before sending emails in Outlook?
In some times, when composing an email in a hurry, you may make a wrong spelling in words and send it without spelling check in Outlook. If there is a method to check spelling before sending emails.
Check spelling before sending
Here is an option can auto check spelling in words before sending messages.

1. Click File > Options. See screenshot:

2. In the Outlook Options dialog, click Mail from left pane, and go to the Compose messages section, check Always check spelling before sending checkbox.
3. Click OK. Now if there are some wrong spelling in your message, after clicking Send button, it will display a dialog to show you the wrong spelling, then you can ignore or change them.
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