HOA is responsible for parking space lines. You might have to go through your landlord for this. Most likely, as a renter, you don't have any standing in the HOA, but some bylaws may allow you to attend meetings and give input.

Community mailbox is going to be owned by the USPS. When I rented an apartment and had mailbox issues, they couldn't do anything about it and could only call the post office. They encouraged me to do the same thing, and eventually (I think a few months) someone fixed the issue. Granted - for ours it was that the lock was broken, cosmetic issues probably won't be addressed. However, to make things more complicated- the peeling paint issue probably goes back to the HOA, depending on who set up the mailbox and how it was built.