Pros
The USPS is a fantastic out of college place to start. You can immdetiealy start moving forward and doing real programming. If you work hard and excel you get noticed and get moved onto more complex and interesting projects. Higher starting wage for out of college in the area and fantastic benefits. You aren't going to find a place with a pension almost anywhere else. Fantastic work/life balance. Paid 1.5x overtime and 2x overtime if above 48 hours a week.
Cons
Lower pay after a few years. Beauracracy abound. Your service partners like DBA's almost never know how you db is set up or works. Theres some dated and strange code that persists for a long time because some people never had to expand themselves. You have some coworkers that are checkout out and dont do much, but they arent bad. Most just nearing retirement and ready to be done. I only ever met one truly terrible person there. Actively avoid all work and insisted on proclaiming how vital they were.