Originally Posted by
hailstorm
Most large post offices have a window open until 3pm on Sunday. You should also be able to just hand the postcards to the hotel front, and they will charge you for and mail the post cards for you.
Most large post offices are open 24 hours a day.
The counters aren't open but the yuuyuu madoguchi is open and you can send things there.
BTW the big post office in Umeda moved 2 years ago to one of the Osaka ekimae (#3 or #4) buildings. It's on the first floor.