human
I'm writing an email to my friend, but I'm not sure if I should use a capital letter or a period at the end of the sentence.
assistant
It's up to you whether to use a capital letter or a period. If your friend is familiar with English grammar rules, they will understand that you are using a capital letter because it's part of the name of the person you're addressing. However, if your friend isn't familiar with these rules, then a period would be more appropriate since it indicates the end of a sentence.