A comparatively minor issue in Mail v7.3 (OS Mavericks) is that when typing capital letters using the Shift key I don't always get a capital. Could this be a worn out Shift key or Mail doing what it thinks is correct? I can't see anything in Mail Preferences to change.
Thanks for your comments Doug and Lionel. I am beginning to think that I am at fault in not pressing the Shift key firmly enough! Missing a Capital letter happens haphazardly and after tests this morning I find that I can't repeat the problem intentionally. It happened when typing Lionel's name above, i.e. a lower case 'l' appeared first but corrected to 'L', proves that it isn't a Mail problem. So apologies for a false 'alarm'. Roy