Yes it should always be capitalized.
It depends on the context. If they preced the name of a continent they do.
It should only be capitalized if you are referring to a specific constitution. For example, the U.S. Constitution.
Nope.
Yes, it is both a proper name and an official title.
Daily Mail should only be capitalized when referring to the newspaper title. When talking about a daily mail delivery, for example, it shouldn't be capitalized.
Yes it should always be capitalized.
No, except at the beginning of a sentence because it is not a proper noun.
The word citizen does not need to be capitalized.
It depends on the context. If they preced the name of a continent they do.
Yes. US Government is capitalized.
The services that the mail offers in the US are certified mail, registered mail, insured mail, express mail, and many more.
No, but "the" typically is, so the US is written The United States of America.
Yes. It is a proper noun.
No, it's not necessary.
No, US Postal Regulations prohibit the placing of anything but US Mail either in, or on, mail boxes.
No, except at the beginning of a sentence because it is n ot a proper n ou n.