Message
for macOS
automatically check and correct spelling mistakes while you're typing. This is a handy feature but for someone like me who don't always type in perfect English on purpose, it's more of a nuisance. Even more so is for those who communicate via other English or Roman alphabet-based languages.
Autocorrect for Message
in macOS
can be disabled from Finder
's configuration menu.
Edit
at the Message
menu. Spelling and Grammar
option. Correct Spelling Automatically
to remove the tick mark. Comment anonymously. Login not required.