There are a few differences between email and post offices, some more obvious than others. For example, the delivery of email is near instantaneous while physical mail via the post office can take days or longer depending on how far the destination is. Another difference is you don’t need to buy stamps in order to send email. You’re also limited to sending digital items via email, while you’re limited to physical goods (which may also contain digital in them like USBs) through post offices. Also, the manpower required to run a post office may surpass the manpower required to maintain the servers and routers involved in the email system. That said, emails can be sent anytime while post offices will open and close at certain times of the day.
Furthermore, there is an assumption that post offices are for older people. Probably by association with technology being difficult for older people to adopt. During my most recent visit to the post office, I found this assumption to be somewhat true.
I had been away from the house when the UPS came by my house with a package that required my signature. Thus, I was required to go to the post office to retrieve my package. Once I had arrived, I took my place in line. Not everyone in line was old, but some were, and the oldest gentleman made his presence the most felt. In response to the speed of the line, I could hear him behind me exclaim “What’s taking so long? Don’t these people have jobs?” Although I would like to think he was referring to the post office workers, he seemed to be facing everyone else, so perhaps not.
Of course there are also similarities which exist between email and post offices. Just like how mail must go through multiple post offices before it reaches its destination, email must go through multiple points before reaching its destination. Also, Post office mail and Email usually requires knowledge of written language during some part of the delivery, reception, or reading of the mail.