Email messages should be treated as personal letters. You wouldn’t write a handwritten letter with misspellings, would you? Or a typewritten letter in which you didn’t bother to use the shift key? Then you shouldn’t do that in an email. Doing so implies to many readers that you don’t respect them enough to bother with such “niceties”.
On a related topic, by convention, words in all caps in email messages are to be read as if the author were shouting them. This is typically not the intended interpretation. According to RFC 1855:
Use symbols for emphasis. That *is* what I meant. Use underscores for underlining. _War and Peace_ is my favorite book.