Hi JayMacy
Letters/emails can have legal words splashed across them (eg, 'without prejudice' in settlement negotiations) however the legal value of such words depends on the context in which they arise
The words 'private and confidential' can be written on an envelope, or email subject line or header, simply to emphasise that the intended recipient should open the letter or (in your case) email, not someone else in whose hands it may unwittingly fall. You can ask your landlord if the words were used in this sense; if he or she says they were intended to have some legal meaning, you can ask him to explain on what basis he or she considers the email contents to be confidential. Generally you don't have a duty to keep information confidential unless there's a confidentiality agreement or something similar in place
Feel welcome to ask any further questions you may have if any of that is unclear, or otherwise
Hugh