Hello, I recently began working for USPS and am interested in learning more. Specifically, I would like to know about its historical origins during the colonial era, its evolution over time, & the eventual dissolution of the Post Office Dept. with the reorganization & creation of the Postal Service. Are there any thorough books you can recommend? Thank you for the help.
The very best scholarly work I know of from recently is The Postal Age: The Emergence of Modern Communications in Nineteenth-Century America by David M. Henkin, which goes into detail about the transition in the mid-19th century of the postal service into widespread use, and the informal networks that ran alongside the post office prior to that. ("Receiving a letter was, for most Americans, an event rather than a feature of ordinary experience.")
More dated (but containing some information not elsewhere) is A Short History of the Mail Service by Carl H. Scheele, which has the advantage of there being a version you can borrow on the Internet Archive.
From the USPS itself there is the eBook
The United States Postal Service, An American History 1775 – 2006
which has some very good pictures as well as an extensive bibliography.
Finally, I recently wrote about the introduction of ZIP codes and the conspiracy theories that developed (and the very odd public service announcements that were made).
Regarding the establishment: Why did the USA's founding fathers feel the Post Office was so important it needed to be in the constitution? written by u/agianttardigrade and u/alraban and u/Spin__Doctor and u/Takeoffdpantsnjaket. Note that u/Spin__Doctor recommends a book at the start of their answer as well.