Does anybody know if you can do this automatically as it would save a huge amount of time
eM Client only does the first letter of a sentence. For anything else, you will need a text replacement application. I use one that automatically replaces some words that I regularly misspell, which is very useful for unusual capitalization like eM Client. And it does other cool things like contractions as well.
A good place to look is this article. It was published nearly two years back, but the applications, and their rankings haven’t changed much. The first in the list is excellent for auto-correction.