if you were saying senor or senora or senorita with a name (like 'mr. smith') is the first letter capitalized?
Sr. Herrera, Sra. Herrera, Srta. Herrera. Works just as in English.
Yes, you should always capitalize it. If you are talking to the person: Hola, Sr. Smith. If you are talking about him, you need the article: el Sr. Smith dice que... Hope this helps.
HI marisa, please read your PM, I will not allow you to continue posting unless you respect the rules of this site for correct spelling and capitalization, thanks.