No idea why this is being downvoted, because it's correct. You can't publish letters without permission. This has been tested in court many times.
What you can do is sell the physical object. That belongs to you.
You can also burn it or destroy it - which is an interesting edge case.
This really comes down to different kinds of ownership. The whole point of copyright is that creative/cultural/intellectual property rights are a thing, analogous to tangible property but with a different set of legal and commercial rights and obligations.
Electronic media depend on context. ISP and telcos are usually considered common carriers so they don't own the copyright of emails or SMSs.
Social media networks either claim all copyright in full (bad news for you...) or have a specific license clause in the T&Cs which gives them reproduction rights.
Sometimes these are for specific limited purposes, and sometimes they're a blanket sign-away of all exploitation rights. (Bad news for you again.)
Am I correct in assuming that uploading it online for others to see or displaying it for personal non commercial use would be covered under the Fair Use Doctrine?
Also, how does it work if a whistleblower gives a journalist letters that they received from someone else? Is the journalist not allowed to publish them in an article?
If a case comes up in the whistleblower situation, the journalist will claim fair use as a defense. It will be up to the court to decide if it is a legitimate defense. It likely will be.
What you can do is sell the physical object. That belongs to you.
You can also burn it or destroy it - which is an interesting edge case.
This really comes down to different kinds of ownership. The whole point of copyright is that creative/cultural/intellectual property rights are a thing, analogous to tangible property but with a different set of legal and commercial rights and obligations.
Electronic media depend on context. ISP and telcos are usually considered common carriers so they don't own the copyright of emails or SMSs.
Social media networks either claim all copyright in full (bad news for you...) or have a specific license clause in the T&Cs which gives them reproduction rights.
Sometimes these are for specific limited purposes, and sometimes they're a blanket sign-away of all exploitation rights. (Bad news for you again.)