Whilst the spelling check in the Lotus Note client may be useful for some people, it is more of an annoyance to me especially when writing about people, places, projects, or anything else that the built-in spell-checker does not recognize.
So here's how to turn off/disable the instant spell check in the Lotus Notes 8.5 client when sending emails :
1. Go to File, Preferences, Spell Check
2. Uncheck "Enable Instant Spell checking"
Also, while you are reading your emails in the Mail/Inbox tab :
1. From the Action Bar, click Tools, Preferences, go to Mail tab
2. Under "Spell Checking", uncheck "Automatically check mail messages for misspellings before sending"