In either case, you can typically rely on Mozilla Thunderbird's spell checker to catch — and correct — your mistyping. With inline spell checking, it will even do so immediately, as you type.
Check Your Spelling as You Type in Mozilla Thunderbird
To have Mozilla Thunderbird check the spelling in the emails you write as you write them:
- Select Tools | Options... from the menu in Mozilla Thunderbird.
- Go to the Composition category.
- Choose the Spelling tab.
- Make sure Enable spell check as you type is checked.
- Close the preferences window.
While composing an email, you can turn the inline spell checker on or off for just this message by selecting Options | Spell As You Type from the menu.